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 $61.33   12.828%   $69.1974   $69.20   $69.20   $69.20  
  Purchase #2 $195.77   5.203%   $205.9559   $205.96   $205.95   $206.00  
  Purchase #3 $183.55   10.334%   $202.5181   $202.52   $202.50   $202.50  
  Purchase #4 $25.78   11.704%   $28.7973   $28.80   $28.80   $28.80  
  Purchase #5 $154.40   7.438%   $165.8843   $165.88   $165.90   $165.90  
  Purchase #6 $59.38   5.783%   $62.8139   $62.81   $62.80   $62.80  
  Purchase #7 $31.59   5.283%   $33.2589   $33.26   $33.25   $33.30  
  7 purchase totals = $711.80       $768.4258   $768.43   $768.40   $768.50