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 $188.43   8.257%   $203.9887   $203.99   $204.00   $204.00  
  Purchase #2 $114.27   10.282%   $126.0192   $126.02   $126.00   $126.00  
  Purchase #3 $121.35   8.523%   $131.6927   $131.69   $131.70   $131.70  
  Purchase #4 $238.32   11.283%   $265.2096   $265.21   $265.20   $265.20  
  Purchase #5 $26.49   12.222%   $29.7276   $29.73   $29.75   $29.70  
  Purchase #6 $158.80   13.435%   $180.1348   $180.13   $180.15   $180.10  
  Purchase #7 $205.49   6.721%   $219.301   $219.30   $219.30   $219.30  
  7 purchase totals = $1,053.15       $1,156.0736   $1,156.07   $1,156.10   $1,156.00