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 $183.73   4.681%   $192.3304   $192.33   $192.35   $192.30  
  Purchase #2 $65.94   11.771%   $73.7018   $73.70   $73.70   $73.70  
  Purchase #3 $180.94   3.831%   $187.8718   $187.87   $187.85   $187.90  
  Purchase #4 $12.27   3.645%   $12.7172   $12.72   $12.70   $12.70  
  Purchase #5 $166.96   6.376%   $177.6054   $177.61   $177.60   $177.60  
  Purchase #6 $133.33   12.766%   $150.3509   $150.35   $150.35   $150.40  
  Purchase #7 $211.55   8.464%   $229.4556   $229.46   $229.45   $229.50  
  7 purchase totals = $954.72       $1,024.0331   $1,024.04   $1,024.00   $1,024.10