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 $67.53   7.763%   $72.7724   $72.77   $72.75   $72.80  
  Purchase #2 $23.37   6.112%   $24.7984   $24.80   $24.80   $24.80  
  Purchase #3 $107.83   12.647%   $121.4673   $121.47   $121.45   $121.50  
  Purchase #4 $229.45   13.344%   $260.0678   $260.07   $260.05   $260.10  
  Purchase #5 $232.38   7.611%   $250.0664   $250.07   $250.05   $250.10  
  Purchase #6 $243.93   11.701%   $272.4722   $272.47   $272.45   $272.50  
  Purchase #7 $54.31   11.867%   $60.755   $60.76   $60.75   $60.80  
  7 purchase totals = $958.80       $1,062.3995   $1,062.41   $1,062.30   $1,062.60