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 $144.50   6.549%   $153.9633   $153.96   $153.95   $154.00  
  Purchase #2 $109.38   13.143%   $123.7558   $123.76   $123.75   $123.80  
  Purchase #3 $205.76   6.871%   $219.8978   $219.90   $219.90   $219.90  
  Purchase #4 $88.98   4.417%   $92.9102   $92.91   $92.90   $92.90  
  Purchase #5 $215.93   5.628%   $228.0825   $228.08   $228.10   $228.10  
  Purchase #6 $145.34   12.324%   $163.2517   $163.25   $163.25   $163.30  
  Purchase #7 $66.95   5.473%   $70.6142   $70.61   $70.60   $70.60  
  7 purchase totals = $976.84       $1,052.4755   $1,052.47   $1,052.45   $1,052.60