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 $26.27   6.823%   $28.0624   $28.06   $28.05   $28.10  
  Purchase #2 $84.89   11.197%   $94.3951   $94.40   $94.40   $94.40  
  Purchase #3 $219.61   3.218%   $226.677   $226.68   $226.70   $226.70  
  Purchase #4 $95.76   7.347%   $102.7955   $102.80   $102.80   $102.80  
  Purchase #5 $122.80   10.206%   $135.333   $135.33   $135.35   $135.30  
  Purchase #6 $155.85   3.590%   $161.445   $161.45   $161.45   $161.40  
  Purchase #7 $105.29   12.469%   $118.4186   $118.42   $118.40   $118.40  
  7 purchase totals = $810.47       $867.1266   $867.14   $867.15   $867.10