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 $40.63   6.792%   $43.3896   $43.39   $43.40   $43.40  
  Purchase #2 $119.43   5.451%   $125.9401   $125.94   $125.95   $125.90  
  Purchase #3 $180.90   13.113%   $204.6214   $204.62   $204.60   $204.60  
  Purchase #4 $157.80   6.247%   $167.6578   $167.66   $167.65   $167.70  
  Purchase #5 $50.76   5.321%   $53.4609   $53.46   $53.45   $53.50  
  Purchase #6 $180.83   12.354%   $203.1697   $203.17   $203.15   $203.20  
  Purchase #7 $250.63   12.560%   $282.1091   $282.11   $282.10   $282.10  
  7 purchase totals = $980.98       $1,080.3486   $1,080.35   $1,080.30   $1,080.40