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 $217.33   13.583%   $246.8499   $246.85   $246.85   $246.80  
  Purchase #2 $118.63   12.814%   $133.8312   $133.83   $133.85   $133.80  
  Purchase #3 $22.43   4.860%   $23.5201   $23.52   $23.50   $23.50  
  Purchase #4 $49.83   12.775%   $56.1958   $56.20   $56.20   $56.20  
  Purchase #5 $98.37   11.286%   $109.472   $109.47   $109.45   $109.50  
  Purchase #6 $207.67   10.240%   $228.9354   $228.94   $228.95   $228.90  
  Purchase #7 $194.93   13.808%   $221.8459   $221.85   $221.85   $221.80  
  7 purchase totals = $909.19       $1,020.6503   $1,020.66   $1,020.65   $1,020.50