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 $36.99   3.681%   $38.3516   $38.35   $38.35   $38.40  
  Purchase #2 $94.33   6.406%   $100.3728   $100.37   $100.35   $100.40  
  Purchase #3 $5.89   6.781%   $6.2894   $6.29   $6.30   $6.30  
  Purchase #4 $23.66   5.131%   $24.874   $24.87   $24.85   $24.90  
  Purchase #5 $217.54   9.419%   $238.0301   $238.03   $238.05   $238.00  
  Purchase #6 $246.40   3.789%   $255.7361   $255.74   $255.75   $255.70  
  Purchase #7 $79.30   6.562%   $84.5037   $84.50   $84.50   $84.50  
  7 purchase totals = $704.11       $748.1577   $748.15   $748.15   $748.20