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 $157.41   6.574%   $167.7581   $167.76   $167.75   $167.80  
  Purchase #2 $202.68   10.507%   $223.9756   $223.98   $224.00   $224.00  
  Purchase #3 $220.59   5.141%   $231.9305   $231.93   $231.95   $231.90  
  Purchase #4 $177.69   7.124%   $190.3486   $190.35   $190.35   $190.30  
  Purchase #5 $160.72   13.651%   $182.6599   $182.66   $182.65   $182.70  
  Purchase #6 $35.63   11.215%   $39.6259   $39.63   $39.65   $39.60  
  Purchase #7 $248.33   11.693%   $277.3672   $277.37   $277.35   $277.40  
  7 purchase totals = $1,203.05       $1,313.6658   $1,313.68   $1,313.70   $1,313.70