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 $92.70   12.783%   $104.5498   $104.55   $104.55   $104.50  
  Purchase #2 $226.66   9.752%   $248.7639   $248.76   $248.75   $248.80  
  Purchase #3 $142.46   7.478%   $153.1132   $153.11   $153.10   $153.10  
  Purchase #4 $197.59   9.467%   $216.2958   $216.30   $216.30   $216.30  
  Purchase #5 $142.93   10.178%   $157.4774   $157.48   $157.50   $157.50  
  Purchase #6 $61.74   4.386%   $64.4479   $64.45   $64.45   $64.40  
  Purchase #7 $116.37   13.182%   $131.7099   $131.71   $131.70   $131.70  
  7 purchase totals = $980.45       $1,076.3579   $1,076.36   $1,076.35   $1,076.30