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 $182.75   10.522%   $201.979   $201.98   $202.00   $202.00  
  Purchase #2 $5.71   11.127%   $6.3454   $6.35   $6.35   $6.30  
  Purchase #3 $247.28   11.176%   $274.916   $274.92   $274.90   $274.90  
  Purchase #4 $126.44   11.590%   $141.0944   $141.09   $141.10   $141.10  
  Purchase #5 $94.36   7.345%   $101.2907   $101.29   $101.30   $101.30  
  Purchase #6 $121.33   8.613%   $131.7802   $131.78   $131.80   $131.80  
  Purchase #7 $116.98   3.296%   $120.8357   $120.84   $120.85   $120.80  
  7 purchase totals = $894.85       $978.2414   $978.25   $978.30   $978.20