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 $211.67   10.268%   $233.4043   $233.40   $233.40   $233.40  
  Purchase #2 $75.89   11.850%   $84.883   $84.88   $84.90   $84.90  
  Purchase #3 $44.79   8.428%   $48.5649   $48.56   $48.55   $48.60  
  Purchase #4 $210.82   11.735%   $235.5597   $235.56   $235.55   $235.60  
  Purchase #5 $81.25   4.659%   $85.0354   $85.04   $85.05   $85.00  
  Purchase #6 $167.66   3.705%   $173.8718   $173.87   $173.85   $173.90  
  Purchase #7 $124.72   6.357%   $132.6485   $132.65   $132.65   $132.60  
  7 purchase totals = $916.80       $993.9676   $993.96   $993.95   $994.00