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 $212.95   6.708%   $227.2347   $227.23   $227.25   $227.20  
  Purchase #2 $138.99   7.397%   $149.2711   $149.27   $149.25   $149.30  
  Purchase #3 $53.85   10.596%   $59.5559   $59.56   $59.55   $59.60  
  Purchase #4 $99.70   5.110%   $104.7947   $104.79   $104.80   $104.80  
  Purchase #5 $190.45   3.540%   $197.1919   $197.19   $197.20   $197.20  
  Purchase #6 $166.72   12.827%   $188.1052   $188.11   $188.10   $188.10  
  Purchase #7 $246.76   3.745%   $256.0012   $256.00   $256.00   $256.00  
  7 purchase totals = $1,109.42       $1,182.1547   $1,182.15   $1,182.15   $1,182.20