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 $98.89   5.126%   $103.9591   $103.96   $103.95   $104.00  
  Purchase #2 $178.28   9.137%   $194.5694   $194.57   $194.55   $194.60  
  Purchase #3 $234.28   5.653%   $247.5238   $247.52   $247.50   $247.50  
  Purchase #4 $61.88   8.646%   $67.2301   $67.23   $67.25   $67.20  
  Purchase #5 $82.36   12.181%   $92.3923   $92.39   $92.40   $92.40  
  Purchase #6 $141.59   7.347%   $151.9926   $151.99   $152.00   $152.00  
  Purchase #7 $127.98   9.829%   $140.5592   $140.56   $140.55   $140.60  
  7 purchase totals = $925.26       $998.2265   $998.22   $998.20   $998.30