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 $212.28   8.754%   $230.863   $230.86   $230.85   $230.90  
  Purchase #2 $147.90   8.786%   $160.8945   $160.89   $160.90   $160.90  
  Purchase #3 $43.28   12.613%   $48.7389   $48.74   $48.75   $48.70  
  Purchase #4 $209.39   3.738%   $217.217   $217.22   $217.20   $217.20  
  Purchase #5 $37.74   7.857%   $40.7052   $40.71   $40.70   $40.70  
  Purchase #6 $89.31   9.147%   $97.4792   $97.48   $97.50   $97.50  
  Purchase #7 $245.53   10.806%   $272.062   $272.06   $272.05   $272.10  
  7 purchase totals = $985.43       $1,067.9598   $1,067.96   $1,067.95   $1,068.00