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 $72.95   12.550%   $82.1052   $82.11   $82.10   $82.10  
  Purchase #2 $249.45   11.718%   $278.6806   $278.68   $278.70   $278.70  
  Purchase #3 $67.39   12.246%   $75.6426   $75.64   $75.65   $75.60  
  Purchase #4 $181.33   13.355%   $205.5466   $205.55   $205.55   $205.50  
  Purchase #5 $88.26   3.213%   $91.0958   $91.10   $91.10   $91.10  
  Purchase #6 $245.34   4.417%   $256.1767   $256.18   $256.20   $256.20  
  Purchase #7 $191.63   8.457%   $207.8361   $207.84   $207.85   $207.80  
  7 purchase totals = $1,096.35       $1,197.0836   $1,197.10   $1,197.15   $1,197.00