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 $11.44   13.820%   $13.021   $13.02   $13.00   $13.00  
  Purchase #2 $99.92   8.471%   $108.3842   $108.38   $108.40   $108.40  
  Purchase #3 $47.70   11.329%   $53.1039   $53.10   $53.10   $53.10  
  Purchase #4 $245.71   13.178%   $278.0897   $278.09   $278.10   $278.10  
  Purchase #5 $25.62   6.821%   $27.3675   $27.37   $27.35   $27.40  
  Purchase #6 $174.82   3.441%   $180.8356   $180.84   $180.85   $180.80  
  Purchase #7 $182.70   10.430%   $201.7556   $201.76   $201.75   $201.80  
  7 purchase totals = $787.91       $862.5575   $862.56   $862.55   $862.60