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 $155.37   7.699%   $167.3319   $167.33   $167.35   $167.30  
  Purchase #2 $228.71   9.609%   $250.6867   $250.69   $250.70   $250.70  
  Purchase #3 $119.28   11.608%   $133.126   $133.13   $133.15   $133.10  
  Purchase #4 $76.94   5.478%   $81.1548   $81.15   $81.15   $81.20  
  Purchase #5 $79.36   6.180%   $84.2644   $84.26   $84.25   $84.30  
  Purchase #6 $112.65   11.235%   $125.3062   $125.31   $125.30   $125.30  
  Purchase #7 $123.97   4.642%   $129.7247   $129.72   $129.70   $129.70  
  7 purchase totals = $896.28       $971.5947   $971.59   $971.60   $971.60