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 $58.52   5.365%   $61.6596   $61.66   $61.65   $61.70  
  Purchase #2 $158.83   8.107%   $171.7063   $171.71   $171.70   $171.70  
  Purchase #3 $93.68   13.432%   $106.2631   $106.26   $106.25   $106.30  
  Purchase #4 $58.78   13.513%   $66.7229   $66.72   $66.70   $66.70  
  Purchase #5 $57.73   9.195%   $63.0383   $63.04   $63.05   $63.00  
  Purchase #6 $209.60   13.732%   $238.3823   $238.38   $238.40   $238.40  
  Purchase #7 $205.83   6.268%   $218.7314   $218.73   $218.75   $218.70  
  7 purchase totals = $842.97       $926.5039   $926.50   $926.50   $926.50