Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $110.48   11.648%   $123.3487   $123.35   $123.35   $123.30  
  Purchase #2 $184.79   10.263%   $203.755   $203.76   $203.75   $203.80  
  Purchase #3 $157.72   10.483%   $174.2538   $174.25   $174.25   $174.30  
  Purchase #4 $233.56   8.854%   $254.2394   $254.24   $254.25   $254.20  
  Purchase #5 $180.70   6.298%   $192.0805   $192.08   $192.10   $192.10  
  Purchase #6 $144.48   8.829%   $157.2361   $157.24   $157.25   $157.20  
  Purchase #7 $148.48   12.228%   $166.6361   $166.64   $166.65   $166.60  
  7 purchase totals = $1,160.21       $1,271.5496   $1,271.56   $1,271.60   $1,271.50