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 $54.65   11.708%   $61.0484   $61.05   $61.05   $61.00  
  Purchase #2 $178.87   5.738%   $189.1336   $189.13   $189.15   $189.10  
  Purchase #3 $36.80   8.769%   $40.027   $40.03   $40.05   $40.00  
  Purchase #4 $22.86   6.269%   $24.2931   $24.29   $24.30   $24.30  
  Purchase #5 $165.80   6.357%   $176.3399   $176.34   $176.35   $176.30  
  Purchase #6 $77.93   5.277%   $82.0424   $82.04   $82.05   $82.00  
  Purchase #7 $74.96   9.573%   $82.1359   $82.14   $82.15   $82.10  
  7 purchase totals = $611.87       $655.0203   $655.02   $655.10   $654.80