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 $240.54   11.598%   $268.4378   $268.44   $268.45   $268.40  
  Purchase #2 $94.26   4.122%   $98.1454   $98.15   $98.15   $98.10  
  Purchase #3 $177.37   13.713%   $201.6927   $201.69   $201.70   $201.70  
  Purchase #4 $59.95   7.155%   $64.2394   $64.24   $64.25   $64.20  
  Purchase #5 $83.39   5.252%   $87.7696   $87.77   $87.75   $87.80  
  Purchase #6 $246.44   6.603%   $262.7124   $262.71   $262.70   $262.70  
  Purchase #7 $46.54   7.199%   $49.8904   $49.89   $49.90   $49.90  
  7 purchase totals = $948.49       $1,032.8877   $1,032.89   $1,032.90   $1,032.80