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 $146.40   11.520%   $163.2653   $163.27   $163.25   $163.30  
  Purchase #2 $67.66   11.843%   $75.673   $75.67   $75.65   $75.70  
  Purchase #3 $116.39   3.768%   $120.7756   $120.78   $120.80   $120.80  
  Purchase #4 $173.80   4.853%   $182.2345   $182.23   $182.25   $182.20  
  Purchase #5 $111.64   6.167%   $118.5248   $118.52   $118.50   $118.50  
  Purchase #6 $122.66   3.136%   $126.5066   $126.51   $126.50   $126.50  
  Purchase #7 $245.40   4.627%   $256.7547   $256.75   $256.75   $256.80  
  7 purchase totals = $983.95       $1,043.7345   $1,043.73   $1,043.70   $1,043.80