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 $215.75   11.721%   $241.0381   $241.04   $241.05   $241.00  
  Purchase #2 $240.33   4.833%   $251.9451   $251.95   $251.95   $251.90  
  Purchase #3 $97.96   8.552%   $106.3375   $106.34   $106.35   $106.30  
  Purchase #4 $228.69   12.837%   $258.0469   $258.05   $258.05   $258.00  
  Purchase #5 $244.49   3.405%   $252.8149   $252.81   $252.80   $252.80  
  Purchase #6 $241.33   5.652%   $254.97   $254.97   $254.95   $255.00  
  Purchase #7 $23.56   12.819%   $26.5802   $26.58   $26.60   $26.60  
  7 purchase totals = $1,292.11       $1,391.7327   $1,391.74   $1,391.75   $1,391.60