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 $246.76   10.765%   $273.3237   $273.32   $273.30   $273.30  
  Purchase #2 $94.75   3.351%   $97.9251   $97.93   $97.95   $97.90  
  Purchase #3 $227.50   8.234%   $246.2324   $246.23   $246.25   $246.20  
  Purchase #4 $17.84   4.585%   $18.658   $18.66   $18.65   $18.70  
  Purchase #5 $101.86   11.753%   $113.8316   $113.83   $113.85   $113.80  
  Purchase #6 $121.64   9.279%   $132.927   $132.93   $132.95   $132.90  
  Purchase #7 $154.66   6.267%   $164.3525   $164.35   $164.35   $164.40  
  7 purchase totals = $965.01       $1,047.2503   $1,047.25   $1,047.30   $1,047.20