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 $206.85   9.679%   $226.871   $226.87   $226.85   $226.90  
  Purchase #2 $153.89   11.172%   $171.0826   $171.08   $171.10   $171.10  
  Purchase #3 $10.45   11.141%   $11.6142   $11.61   $11.60   $11.60  
  Purchase #4 $47.33   3.380%   $48.9298   $48.93   $48.95   $48.90  
  Purchase #5 $223.34   9.575%   $244.7248   $244.72   $244.70   $244.70  
  Purchase #6 $56.90   10.567%   $62.9126   $62.91   $62.90   $62.90  
  Purchase #7 $153.66   4.492%   $160.5624   $160.56   $160.55   $160.60  
  7 purchase totals = $852.42       $926.6974   $926.68   $926.65   $926.70