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 $187.67   13.830%   $213.6248   $213.62   $213.60   $213.60  
  Purchase #2 $239.41   10.533%   $264.6271   $264.63   $264.65   $264.60  
  Purchase #3 $141.28   8.693%   $153.5615   $153.56   $153.55   $153.60  
  Purchase #4 $164.27   9.807%   $180.38   $180.38   $180.40   $180.40  
  Purchase #5 $244.71   13.431%   $277.577   $277.58   $277.60   $277.60  
  Purchase #6 $111.53   12.792%   $125.7969   $125.80   $125.80   $125.80  
  Purchase #7 $31.26   6.260%   $33.2169   $33.22   $33.20   $33.20  
  7 purchase totals = $1,120.13       $1,248.7842   $1,248.79   $1,248.80   $1,248.80