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 $13.85   6.587%   $14.7623   $14.76   $14.75   $14.80  
  Purchase #2 $231.66   10.180%   $255.243   $255.24   $255.25   $255.20  
  Purchase #3 $180.26   12.214%   $202.277   $202.28   $202.30   $202.30  
  Purchase #4 $246.74   5.356%   $259.9554   $259.96   $259.95   $260.00  
  Purchase #5 $153.39   11.226%   $170.6096   $170.61   $170.60   $170.60  
  Purchase #6 $15.70   8.491%   $17.0331   $17.03   $17.05   $17.00  
  Purchase #7 $58.95   3.610%   $61.0781   $61.08   $61.10   $61.10  
  7 purchase totals = $900.55       $980.9585   $980.96   $981.00   $981.00