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 $89.63   11.113%   $99.5906   $99.59   $99.60   $99.60  
  Purchase #2 $186.92   4.309%   $194.9744   $194.97   $194.95   $195.00  
  Purchase #3 $48.80   3.860%   $50.6837   $50.68   $50.70   $50.70  
  Purchase #4 $61.52   3.161%   $63.4646   $63.46   $63.45   $63.50  
  Purchase #5 $117.98   7.595%   $126.9406   $126.94   $126.95   $126.90  
  Purchase #6 $100.94   12.741%   $113.8008   $113.80   $113.80   $113.80  
  Purchase #7 $123.40   4.445%   $128.8851   $128.89   $128.90   $128.90  
  7 purchase totals = $729.19       $778.3398   $778.33   $778.35   $778.40