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 $53.87   3.411%   $55.7075   $55.71   $55.70   $55.70  
  Purchase #2 $170.79   4.121%   $177.8283   $177.83   $177.85   $177.80  
  Purchase #3 $110.99   13.604%   $126.0891   $126.09   $126.10   $126.10  
  Purchase #4 $127.34   8.208%   $137.7921   $137.79   $137.80   $137.80  
  Purchase #5 $154.94   8.819%   $168.6042   $168.60   $168.60   $168.60  
  Purchase #6 $190.36   8.173%   $205.9181   $205.92   $205.90   $205.90  
  Purchase #7 $160.96   8.738%   $175.0247   $175.02   $175.00   $175.00  
  7 purchase totals = $969.25       $1,046.9640   $1,046.96   $1,046.95   $1,046.90