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 $54.95   7.523%   $59.0839   $59.08   $59.10   $59.10  
  Purchase #2 $249.67   5.818%   $264.1958   $264.20   $264.20   $264.20  
  Purchase #3 $20.45   10.733%   $22.6449   $22.64   $22.65   $22.60  
  Purchase #4 $187.34   10.861%   $207.687   $207.69   $207.70   $207.70  
  Purchase #5 $78.93   13.551%   $89.6258   $89.63   $89.65   $89.60  
  Purchase #6 $145.31   10.468%   $160.5211   $160.52   $160.50   $160.50  
  Purchase #7 $102.26   5.800%   $108.1911   $108.19   $108.20   $108.20  
  7 purchase totals = $838.91       $911.9496   $911.95   $912.00   $911.90