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 $113.29   12.584%   $127.5464   $127.55   $127.55   $127.50  
  Purchase #2 $244.97   7.160%   $262.5099   $262.51   $262.50   $262.50  
  Purchase #3 $84.88   12.282%   $95.305   $95.31   $95.30   $95.30  
  Purchase #4 $61.34   13.233%   $69.4571   $69.46   $69.45   $69.50  
  Purchase #5 $79.27   6.453%   $84.3853   $84.39   $84.40   $84.40  
  Purchase #6 $139.98   4.229%   $145.8998   $145.90   $145.90   $145.90  
  Purchase #7 $108.97   9.209%   $119.005   $119.01   $119.00   $119.00  
  7 purchase totals = $832.70       $904.1085   $904.13   $904.10   $904.10