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 $217.45   13.769%   $247.3907   $247.39   $247.40   $247.40  
  Purchase #2 $8.89   10.527%   $9.8259   $9.83   $9.85   $9.80  
  Purchase #3 $113.26   5.526%   $119.5187   $119.52   $119.50   $119.50  
  Purchase #4 $40.80   6.603%   $43.494   $43.49   $43.50   $43.50  
  Purchase #5 $202.83   8.411%   $219.89   $219.89   $219.90   $219.90  
  Purchase #6 $164.48   8.369%   $178.2453   $178.25   $178.25   $178.20  
  Purchase #7 $6.92   10.380%   $7.6383   $7.64   $7.65   $7.60  
  7 purchase totals = $754.63       $826.0029   $826.01   $826.05   $825.90