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 $219.82   11.688%   $245.5126   $245.51   $245.50   $245.50  
  Purchase #2 $81.91   3.461%   $84.7449   $84.74   $84.75   $84.70  
  Purchase #3 $74.37   13.595%   $84.4806   $84.48   $84.50   $84.50  
  Purchase #4 $53.92   11.605%   $60.1774   $60.18   $60.20   $60.20  
  Purchase #5 $179.54   11.873%   $200.8568   $200.86   $200.85   $200.90  
  Purchase #6 $228.62   6.824%   $244.221   $244.22   $244.20   $244.20  
  Purchase #7 $24.61   4.578%   $25.7366   $25.74   $25.75   $25.70  
  7 purchase totals = $862.79       $945.7299   $945.73   $945.75   $945.70