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 $87.60   8.111%   $94.7052   $94.71   $94.70   $94.70  
  Purchase #2 $84.41   7.864%   $91.048   $91.05   $91.05   $91.00  
  Purchase #3 $103.59   13.457%   $117.5301   $117.53   $117.55   $117.50  
  Purchase #4 $245.74   4.371%   $256.4813   $256.48   $256.50   $256.50  
  Purchase #5 $93.41   13.511%   $106.0306   $106.03   $106.05   $106.00  
  Purchase #6 $119.84   10.284%   $132.1643   $132.16   $132.15   $132.20  
  Purchase #7 $43.30   8.806%   $47.113   $47.11   $47.10   $47.10  
  7 purchase totals = $777.89       $845.0725   $845.07   $845.10   $845.00