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 $109.50   8.716%   $119.044   $119.04   $119.05   $119.00  
  Purchase #2 $55.38   7.688%   $59.6376   $59.64   $59.65   $59.60  
  Purchase #3 $175.89   5.155%   $184.9571   $184.96   $184.95   $185.00  
  Purchase #4 $52.35   3.171%   $54.01   $54.01   $54.00   $54.00  
  Purchase #5 $101.26   8.414%   $109.78   $109.78   $109.80   $109.80  
  Purchase #6 $200.66   3.754%   $208.1928   $208.19   $208.20   $208.20  
  Purchase #7 $52.95   6.577%   $56.4325   $56.43   $56.45   $56.40  
  7 purchase totals = $747.99       $792.0540   $792.05   $792.10   $792.00