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 $55.32   12.250%   $62.0967   $62.10   $62.10   $62.10  
  Purchase #2 $236.98   3.238%   $244.6534   $244.65   $244.65   $244.70  
  Purchase #3 $243.90   12.311%   $273.9265   $273.93   $273.95   $273.90  
  Purchase #4 $6.55   11.151%   $7.2804   $7.28   $7.30   $7.30  
  Purchase #5 $57.63   3.374%   $59.5744   $59.57   $59.55   $59.60  
  Purchase #6 $12.96   9.120%   $14.142   $14.14   $14.15   $14.10  
  Purchase #7 $164.98   9.355%   $180.4139   $180.41   $180.40   $180.40  
  7 purchase totals = $778.32       $842.0873   $842.08   $842.10   $842.10