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 $111.78   13.163%   $126.4936   $126.49   $126.50   $126.50  
  Purchase #2 $225.94   7.686%   $243.3057   $243.31   $243.30   $243.30  
  Purchase #3 $53.40   3.669%   $55.3592   $55.36   $55.35   $55.40  
  Purchase #4 $234.45   12.873%   $264.6307   $264.63   $264.65   $264.60  
  Purchase #5 $105.77   13.280%   $119.8163   $119.82   $119.80   $119.80  
  Purchase #6 $177.46   7.427%   $190.64   $190.64   $190.65   $190.60  
  Purchase #7 $184.68   9.221%   $201.7093   $201.71   $201.70   $201.70  
  7 purchase totals = $1,093.48       $1,201.9548   $1,201.96   $1,201.95   $1,201.90