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 $53.27   10.685%   $58.9619   $58.96   $58.95   $59.00  
  Purchase #2 $28.42   11.435%   $31.6698   $31.67   $31.65   $31.70  
  Purchase #3 $157.55   11.344%   $175.4225   $175.42   $175.40   $175.40  
  Purchase #4 $203.36   7.859%   $219.3421   $219.34   $219.35   $219.30  
  Purchase #5 $226.38   7.423%   $243.1842   $243.18   $243.20   $243.20  
  Purchase #6 $250.55   4.535%   $261.9124   $261.91   $261.90   $261.90  
  Purchase #7 $76.94   9.846%   $84.5155   $84.52   $84.50   $84.50  
  7 purchase totals = $996.47       $1,075.0084   $1,075.00   $1,074.95   $1,075.00