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 $23.74   6.754%   $25.3434   $25.34   $25.35   $25.30  
  Purchase #2 $210.38   7.144%   $225.4095   $225.41   $225.40   $225.40  
  Purchase #3 $155.65   9.183%   $169.9433   $169.94   $169.95   $169.90  
  Purchase #4 $229.85   8.824%   $250.132   $250.13   $250.15   $250.10  
  Purchase #5 $54.40   13.754%   $61.8822   $61.88   $61.90   $61.90  
  Purchase #6 $145.49   3.163%   $150.0918   $150.09   $150.10   $150.10  
  Purchase #7 $65.52   13.755%   $74.5323   $74.53   $74.55   $74.50  
  7 purchase totals = $885.03       $957.3345   $957.32   $957.40   $957.20