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 $55.42   8.319%   $60.0304   $60.03   $60.05   $60.00  
  Purchase #2 $238.79   11.643%   $266.5923   $266.59   $266.60   $266.60  
  Purchase #3 $139.41   7.506%   $149.8741   $149.87   $149.85   $149.90  
  Purchase #4 $57.33   12.410%   $64.4447   $64.44   $64.45   $64.40  
  Purchase #5 $51.30   11.260%   $57.0764   $57.08   $57.10   $57.10  
  Purchase #6 $170.50   8.126%   $184.3548   $184.35   $184.35   $184.40  
  Purchase #7 $85.90   9.699%   $94.2314   $94.23   $94.25   $94.20  
  7 purchase totals = $798.65       $876.6041   $876.59   $876.65   $876.60