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 $13.74   8.851%   $14.9561   $14.96   $14.95   $15.00  
  Purchase #2 $219.43   12.242%   $246.2926   $246.29   $246.30   $246.30  
  Purchase #3 $246.73   10.764%   $273.288   $273.29   $273.30   $273.30  
  Purchase #4 $174.55   12.724%   $196.7597   $196.76   $196.75   $196.80  
  Purchase #5 $110.83   7.564%   $119.2132   $119.21   $119.20   $119.20  
  Purchase #6 $211.82   11.607%   $236.4059   $236.41   $236.40   $236.40  
  Purchase #7 $156.37   11.790%   $174.806   $174.81   $174.80   $174.80  
  7 purchase totals = $1,133.47       $1,261.7215   $1,261.73   $1,261.70   $1,261.80