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 $103.47   10.104%   $113.9246   $113.92   $113.90   $113.90  
  Purchase #2 $216.74   8.633%   $235.4512   $235.45   $235.45   $235.50  
  Purchase #3 $164.39   13.721%   $186.946   $186.95   $186.95   $186.90  
  Purchase #4 $147.50   9.392%   $161.3532   $161.35   $161.35   $161.40  
  Purchase #5 $94.42   3.476%   $97.702   $97.70   $97.70   $97.70  
  Purchase #6 $117.92   8.569%   $128.0246   $128.02   $128.00   $128.00  
  Purchase #7 $104.90   3.794%   $108.8799   $108.88   $108.90   $108.90  
  7 purchase totals = $949.34       $1,032.2815   $1,032.27   $1,032.25   $1,032.30