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 $110.96   6.675%   $118.3666   $118.37   $118.35   $118.40  
  Purchase #2 $179.60   4.319%   $187.3569   $187.36   $187.35   $187.40  
  Purchase #3 $62.82   6.554%   $66.9372   $66.94   $66.95   $66.90  
  Purchase #4 $30.49   8.845%   $33.1868   $33.19   $33.20   $33.20  
  Purchase #5 $246.48   6.733%   $263.0755   $263.08   $263.10   $263.10  
  Purchase #6 $220.95   6.725%   $235.8089   $235.81   $235.80   $235.80  
  Purchase #7 $52.62   3.455%   $54.438   $54.44   $54.45   $54.40  
  7 purchase totals = $903.92       $959.1699   $959.19   $959.20   $959.20