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 $211.53   8.236%   $228.9516   $228.95   $228.95   $229.00  
  Purchase #2 $176.83   11.603%   $197.3476   $197.35   $197.35   $197.30  
  Purchase #3 $202.97   11.385%   $226.0781   $226.08   $226.10   $226.10  
  Purchase #4 $87.44   9.163%   $95.4521   $95.45   $95.45   $95.50  
  Purchase #5 $54.40   4.110%   $56.6358   $56.64   $56.65   $56.60  
  Purchase #6 $92.96   10.714%   $102.9197   $102.92   $102.90   $102.90  
  Purchase #7 $68.49   11.316%   $76.2403   $76.24   $76.25   $76.20  
  7 purchase totals = $894.62       $983.6252   $983.63   $983.65   $983.60