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 $95.67   11.590%   $106.7582   $106.76   $106.75   $106.80  
  Purchase #2 $17.52   11.789%   $19.5854   $19.59   $19.60   $19.60  
  Purchase #3 $143.95   12.557%   $162.0258   $162.03   $162.05   $162.00  
  Purchase #4 $243.35   10.218%   $268.2155   $268.22   $268.20   $268.20  
  Purchase #5 $46.43   9.160%   $50.683   $50.68   $50.70   $50.70  
  Purchase #6 $44.98   6.444%   $47.8785   $47.88   $47.90   $47.90  
  Purchase #7 $63.75   12.696%   $71.8437   $71.84   $71.85   $71.80  
  7 purchase totals = $655.65       $726.9901   $727.00   $727.05   $727.00