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 $182.47   11.784%   $203.9723   $203.97   $203.95   $204.00  
  Purchase #2 $241.81   10.647%   $267.5555   $267.56   $267.55   $267.60  
  Purchase #3 $243.25   13.291%   $275.5804   $275.58   $275.60   $275.60  
  Purchase #4 $11.80   4.839%   $12.371   $12.37   $12.35   $12.40  
  Purchase #5 $27.46   9.179%   $29.9806   $29.98   $30.00   $30.00  
  Purchase #6 $53.39   10.588%   $59.0429   $59.04   $59.05   $59.00  
  Purchase #7 $117.75   13.636%   $133.8064   $133.81   $133.80   $133.80  
  7 purchase totals = $877.93       $982.3091   $982.31   $982.30   $982.40