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 $207.91   12.825%   $234.5745   $234.57   $234.55   $234.60  
  Purchase #2 $157.54   10.266%   $173.7131   $173.71   $173.70   $173.70  
  Purchase #3 $31.37   11.791%   $35.0688   $35.07   $35.05   $35.10  
  Purchase #4 $203.51   7.644%   $219.0663   $219.07   $219.05   $219.10  
  Purchase #5 $192.95   8.345%   $209.0517   $209.05   $209.05   $209.10  
  Purchase #6 $42.33   11.381%   $47.1476   $47.15   $47.15   $47.10  
  Purchase #7 $227.60   10.305%   $251.0542   $251.05   $251.05   $251.10  
  7 purchase totals = $1,063.21       $1,169.6762   $1,169.67   $1,169.60   $1,169.80