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 $36.52   12.388%   $41.0441   $41.04   $41.05   $41.00  
  Purchase #2 $106.95   10.189%   $117.8471   $117.85   $117.85   $117.80  
  Purchase #3 $52.41   5.572%   $55.3303   $55.33   $55.35   $55.30  
  Purchase #4 $63.78   7.224%   $68.3875   $68.39   $68.40   $68.40  
  Purchase #5 $44.81   8.480%   $48.6099   $48.61   $48.60   $48.60  
  Purchase #6 $222.59   9.747%   $244.2858   $244.29   $244.30   $244.30  
  Purchase #7 $149.25   8.553%   $162.0154   $162.02   $162.00   $162.00  
  7 purchase totals = $676.31       $737.5201   $737.53   $737.55   $737.40