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 $87.73   12.441%   $98.6445   $98.64   $98.65   $98.60  
  Purchase #2 $167.39   13.804%   $190.4965   $190.50   $190.50   $190.50  
  Purchase #3 $68.65   4.200%   $71.5333   $71.53   $71.55   $71.50  
  Purchase #4 $216.66   3.254%   $223.7101   $223.71   $223.70   $223.70  
  Purchase #5 $61.55   8.595%   $66.8402   $66.84   $66.85   $66.80  
  Purchase #6 $36.75   4.732%   $38.489   $38.49   $38.50   $38.50  
  Purchase #7 $55.54   8.734%   $60.3909   $60.39   $60.40   $60.40  
  7 purchase totals = $694.27       $750.1045   $750.10   $750.15   $750.00