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 $62.73   11.846%   $70.161   $70.16   $70.15   $70.20  
  Purchase #2 $225.82   7.837%   $243.5175   $243.52   $243.50   $243.50  
  Purchase #3 $150.54   11.663%   $168.0975   $168.10   $168.10   $168.10  
  Purchase #4 $16.44   9.115%   $17.9385   $17.94   $17.95   $17.90  
  Purchase #5 $103.76   12.188%   $116.4063   $116.41   $116.40   $116.40  
  Purchase #6 $93.45   13.779%   $106.3265   $106.33   $106.35   $106.30  
  Purchase #7 $47.90   5.367%   $50.4708   $50.47   $50.45   $50.50  
  7 purchase totals = $700.64       $772.9181   $772.93   $772.90   $772.90