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 $219.63   13.765%   $249.8621   $249.86   $249.85   $249.90  
  Purchase #2 $217.55   5.785%   $230.1353   $230.14   $230.15   $230.10  
  Purchase #3 $22.96   5.726%   $24.2747   $24.27   $24.25   $24.30  
  Purchase #4 $197.72   7.512%   $212.5727   $212.57   $212.55   $212.60  
  Purchase #5 $159.93   8.864%   $174.1062   $174.11   $174.10   $174.10  
  Purchase #6 $220.52   10.807%   $244.3516   $244.35   $244.35   $244.40  
  Purchase #7 $151.75   9.258%   $165.799   $165.80   $165.80   $165.80  
  7 purchase totals = $1,190.06       $1,301.1016   $1,301.10   $1,301.05   $1,301.20