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 $203.42   10.127%   $224.0203   $224.02   $224.00   $224.00  
  Purchase #2 $170.82   10.219%   $188.2761   $188.28   $188.30   $188.30  
  Purchase #3 $206.71   8.704%   $224.702   $224.70   $224.70   $224.70  
  Purchase #4 $53.48   13.692%   $60.8025   $60.80   $60.80   $60.80  
  Purchase #5 $23.35   9.637%   $25.6002   $25.60   $25.60   $25.60  
  Purchase #6 $206.68   6.534%   $220.1845   $220.18   $220.20   $220.20  
  Purchase #7 $192.36   9.598%   $210.8227   $210.82   $210.80   $210.80  
  7 purchase totals = $1,056.82       $1,154.4083   $1,154.40   $1,154.40   $1,154.40