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 $75.63   3.403%   $78.2037   $78.20   $78.20   $78.20  
  Purchase #2 $56.66   3.859%   $58.8465   $58.85   $58.85   $58.80  
  Purchase #3 $80.74   4.435%   $84.3208   $84.32   $84.30   $84.30  
  Purchase #4 $249.27   8.411%   $270.2361   $270.24   $270.25   $270.20  
  Purchase #5 $197.43   3.477%   $204.2946   $204.29   $204.30   $204.30  
  Purchase #6 $179.91   4.245%   $187.5472   $187.55   $187.55   $187.50  
  Purchase #7 $118.83   10.666%   $131.5044   $131.50   $131.50   $131.50  
  7 purchase totals = $958.47       $1,014.9533   $1,014.95   $1,014.95   $1,014.80