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 $90.88   11.692%   $101.5057   $101.51   $101.50   $101.50  
  Purchase #2 $213.26   13.324%   $241.6748   $241.67   $241.65   $241.70  
  Purchase #3 $111.36   11.563%   $124.2366   $124.24   $124.25   $124.20  
  Purchase #4 $183.31   3.185%   $189.1484   $189.15   $189.15   $189.10  
  Purchase #5 $139.91   6.414%   $148.8838   $148.88   $148.90   $148.90  
  Purchase #6 $147.49   12.289%   $165.615   $165.62   $165.60   $165.60  
  Purchase #7 $85.54   10.185%   $94.2522   $94.25   $94.25   $94.30  
  7 purchase totals = $971.75       $1,065.3165   $1,065.32   $1,065.30   $1,065.30