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 $67.34   12.670%   $75.872   $75.87   $75.85   $75.90  
  Purchase #2 $144.72   3.623%   $149.9632   $149.96   $149.95   $150.00  
  Purchase #3 $65.67   11.860%   $73.4585   $73.46   $73.45   $73.50  
  Purchase #4 $111.68   5.393%   $117.7029   $117.70   $117.70   $117.70  
  Purchase #5 $27.69   6.227%   $29.4143   $29.41   $29.40   $29.40  
  Purchase #6 $125.90   5.605%   $132.9567   $132.96   $132.95   $133.00  
  Purchase #7 $17.65   7.643%   $18.999   $19.00   $19.00   $19.00  
  7 purchase totals = $560.65       $598.3666   $598.36   $598.30   $598.50