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 $102.82   10.831%   $113.9564   $113.96   $113.95   $114.00  
  Purchase #2 $62.52   5.534%   $65.9799   $65.98   $66.00   $66.00  
  Purchase #3 $58.85   7.528%   $63.2802   $63.28   $63.30   $63.30  
  Purchase #4 $232.77   7.563%   $250.3744   $250.37   $250.35   $250.40  
  Purchase #5 $115.47   9.134%   $126.017   $126.02   $126.00   $126.00  
  Purchase #6 $93.88   3.383%   $97.056   $97.06   $97.05   $97.10  
  Purchase #7 $239.30   5.415%   $252.2581   $252.26   $252.25   $252.30  
  7 purchase totals = $905.61       $968.9220   $968.93   $968.90   $969.10