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 $126.59   6.630%   $134.9829   $134.98   $135.00   $135.00  
  Purchase #2 $199.63   4.147%   $207.9087   $207.91   $207.90   $207.90  
  Purchase #3 $119.75   5.698%   $126.5734   $126.57   $126.55   $126.60  
  Purchase #4 $159.44   13.815%   $181.4666   $181.47   $181.45   $181.50  
  Purchase #5 $159.82   7.355%   $171.5748   $171.57   $171.55   $171.60  
  Purchase #6 $240.90   6.324%   $256.1345   $256.13   $256.15   $256.10  
  Purchase #7 $156.88   10.303%   $173.0433   $173.04   $173.05   $173.00  
  7 purchase totals = $1,163.01       $1,251.6842   $1,251.67   $1,251.65   $1,251.70