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 $10.34   11.263%   $11.5046   $11.50   $11.50   $11.50  
  Purchase #2 $77.93   10.386%   $86.0238   $86.02   $86.00   $86.00  
  Purchase #3 $112.73   9.704%   $123.6693   $123.67   $123.65   $123.70  
  Purchase #4 $198.34   7.786%   $213.7828   $213.78   $213.80   $213.80  
  Purchase #5 $25.36   13.642%   $28.8196   $28.82   $28.80   $28.80  
  Purchase #6 $163.82   11.191%   $182.1531   $182.15   $182.15   $182.20  
  Purchase #7 $188.65   6.226%   $200.3953   $200.40   $200.40   $200.40  
  7 purchase totals = $777.17       $846.3485   $846.34   $846.30   $846.40