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 $246.62   10.361%   $272.1723   $272.17   $272.15   $272.20  
  Purchase #2 $246.30   6.766%   $262.9647   $262.96   $262.95   $263.00  
  Purchase #3 $209.34   6.242%   $222.407   $222.41   $222.40   $222.40  
  Purchase #4 $247.47   8.248%   $267.8813   $267.88   $267.90   $267.90  
  Purchase #5 $203.26   11.331%   $226.2914   $226.29   $226.30   $226.30  
  Purchase #6 $76.68   6.476%   $81.6458   $81.65   $81.65   $81.60  
  Purchase #7 $37.97   3.296%   $39.2215   $39.22   $39.20   $39.20  
  7 purchase totals = $1,267.64       $1,372.5840   $1,372.58   $1,372.55   $1,372.60