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 $242.35   6.713%   $258.619   $258.62   $258.60   $258.60  
  Purchase #2 $202.97   9.854%   $222.9707   $222.97   $222.95   $223.00  
  Purchase #3 $67.87   11.748%   $75.8434   $75.84   $75.85   $75.80  
  Purchase #4 $45.70   6.347%   $48.6006   $48.60   $48.60   $48.60  
  Purchase #5 $113.97   3.799%   $118.2997   $118.30   $118.30   $118.30  
  Purchase #6 $114.88   5.313%   $120.9836   $120.98   $121.00   $121.00  
  Purchase #7 $92.91   5.769%   $98.27   $98.27   $98.25   $98.30  
  7 purchase totals = $880.65       $943.5870   $943.58   $943.55   $943.60