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 $208.59   8.682%   $226.6998   $226.70   $226.70   $226.70  
  Purchase #2 $201.47   13.347%   $228.3602   $228.36   $228.35   $228.40  
  Purchase #3 $17.69   5.327%   $18.6323   $18.63   $18.65   $18.60  
  Purchase #4 $80.51   9.359%   $88.0449   $88.04   $88.05   $88.00  
  Purchase #5 $205.51   13.364%   $232.9744   $232.97   $232.95   $233.00  
  Purchase #6 $228.71   9.361%   $250.1195   $250.12   $250.10   $250.10  
  Purchase #7 $22.49   5.855%   $23.8068   $23.81   $23.80   $23.80  
  7 purchase totals = $964.97       $1,068.6379   $1,068.63   $1,068.60   $1,068.60