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 $117.62   13.604%   $133.621   $133.62   $133.60   $133.60  
  Purchase #2 $180.28   6.672%   $192.3083   $192.31   $192.30   $192.30  
  Purchase #3 $143.30   9.318%   $156.6527   $156.65   $156.65   $156.70  
  Purchase #4 $69.72   7.652%   $75.055   $75.06   $75.05   $75.10  
  Purchase #5 $44.74   5.731%   $47.304   $47.30   $47.30   $47.30  
  Purchase #6 $244.55   10.226%   $269.5577   $269.56   $269.55   $269.60  
  Purchase #7 $149.47   8.823%   $162.6577   $162.66   $162.65   $162.70  
  7 purchase totals = $949.68       $1,037.1564   $1,037.16   $1,037.10   $1,037.30