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 $110.63   13.627%   $125.7056   $125.71   $125.70   $125.70  
  Purchase #2 $195.75   3.771%   $203.1317   $203.13   $203.15   $203.10  
  Purchase #3 $189.57   9.487%   $207.5545   $207.55   $207.55   $207.60  
  Purchase #4 $32.89   7.745%   $35.4373   $35.44   $35.45   $35.40  
  Purchase #5 $151.28   10.369%   $166.9662   $166.97   $166.95   $167.00  
  Purchase #6 $157.71   6.165%   $167.4328   $167.43   $167.45   $167.40  
  Purchase #7 $51.47   6.411%   $54.7697   $54.77   $54.75   $54.80  
  7 purchase totals = $889.30       $960.9978   $961.00   $961.00   $961.00