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 $58.96   13.647%   $67.0063   $67.01   $67.00   $67.00  
  Purchase #2 $41.73   5.803%   $44.1516   $44.15   $44.15   $44.20  
  Purchase #3 $177.76   12.190%   $199.4289   $199.43   $199.45   $199.40  
  Purchase #4 $22.87   7.392%   $24.5606   $24.56   $24.55   $24.60  
  Purchase #5 $104.75   5.115%   $110.108   $110.11   $110.10   $110.10  
  Purchase #6 $82.50   13.589%   $93.7109   $93.71   $93.70   $93.70  
  Purchase #7 $42.51   4.796%   $44.5488   $44.55   $44.55   $44.50  
  7 purchase totals = $531.08       $583.5151   $583.52   $583.50   $583.50