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 $47.75   12.275%   $53.6113   $53.61   $53.60   $53.60  
  Purchase #2 $211.84   10.788%   $234.6933   $234.69   $234.70   $234.70  
  Purchase #3 $123.81   9.251%   $135.2637   $135.26   $135.25   $135.30  
  Purchase #4 $179.68   4.739%   $188.195   $188.20   $188.20   $188.20  
  Purchase #5 $181.61   6.707%   $193.7906   $193.79   $193.80   $193.80  
  Purchase #6 $118.30   10.785%   $131.0587   $131.06   $131.05   $131.10  
  Purchase #7 $238.61   8.320%   $258.4624   $258.46   $258.45   $258.50  
  7 purchase totals = $1,101.60       $1,195.0750   $1,195.07   $1,195.05   $1,195.20