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 $231.56   7.111%   $248.0262   $248.03   $248.05   $248.00  
  Purchase #2 $87.73   4.611%   $91.7752   $91.78   $91.80   $91.80  
  Purchase #3 $111.32   5.478%   $117.4181   $117.42   $117.40   $117.40  
  Purchase #4 $195.94   5.827%   $207.3574   $207.36   $207.35   $207.40  
  Purchase #5 $71.57   6.634%   $76.318   $76.32   $76.30   $76.30  
  Purchase #6 $106.46   13.549%   $120.8843   $120.88   $120.90   $120.90  
  Purchase #7 $186.26   9.207%   $203.409   $203.41   $203.40   $203.40  
  7 purchase totals = $990.84       $1,065.1882   $1,065.20   $1,065.20   $1,065.20