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 $100.78   9.692%   $110.5476   $110.55   $110.55   $110.50  
  Purchase #2 $171.89   10.508%   $189.9522   $189.95   $189.95   $190.00  
  Purchase #3 $192.97   13.757%   $219.5169   $219.52   $219.50   $219.50  
  Purchase #4 $131.82   8.729%   $143.3266   $143.33   $143.35   $143.30  
  Purchase #5 $64.88   10.102%   $71.4342   $71.43   $71.45   $71.40  
  Purchase #6 $125.55   3.497%   $129.9405   $129.94   $129.95   $129.90  
  Purchase #7 $220.81   7.125%   $236.5427   $236.54   $236.55   $236.50  
  7 purchase totals = $1,008.70       $1,101.2607   $1,101.26   $1,101.30   $1,101.10