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 $77.31   9.174%   $84.4024   $84.40   $84.40   $84.40  
  Purchase #2 $92.39   13.568%   $104.9255   $104.93   $104.95   $104.90  
  Purchase #3 $241.44   4.568%   $252.469   $252.47   $252.45   $252.50  
  Purchase #4 $191.53   10.135%   $210.9416   $210.94   $210.95   $210.90  
  Purchase #5 $11.33   11.802%   $12.6672   $12.67   $12.65   $12.70  
  Purchase #6 $201.37   5.396%   $212.2359   $212.24   $212.25   $212.20  
  Purchase #7 $69.59   4.744%   $72.8913   $72.89   $72.90   $72.90  
  7 purchase totals = $884.96       $950.5329   $950.54   $950.55   $950.50