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 $12.84   9.129%   $14.0122   $14.01   $14.00   $14.00  
  Purchase #2 $181.40   13.854%   $206.5312   $206.53   $206.55   $206.50  
  Purchase #3 $148.36   4.286%   $154.7187   $154.72   $154.70   $154.70  
  Purchase #4 $94.93   9.377%   $103.8316   $103.83   $103.85   $103.80  
  Purchase #5 $213.54   8.452%   $231.5884   $231.59   $231.60   $231.60  
  Purchase #6 $129.33   11.593%   $144.3232   $144.32   $144.30   $144.30  
  Purchase #7 $146.50   13.785%   $166.695   $166.70   $166.70   $166.70  
  7 purchase totals = $926.90       $1,021.7003   $1,021.70   $1,021.70   $1,021.60