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 $61.53   12.304%   $69.1007   $69.10   $69.10   $69.10  
  Purchase #2 $176.87   10.448%   $195.3494   $195.35   $195.35   $195.30  
  Purchase #3 $60.90   9.713%   $66.8152   $66.82   $66.80   $66.80  
  Purchase #4 $144.48   10.253%   $159.2935   $159.29   $159.30   $159.30  
  Purchase #5 $25.68   13.522%   $29.1524   $29.15   $29.15   $29.20  
  Purchase #6 $152.84   7.456%   $164.2358   $164.24   $164.25   $164.20  
  Purchase #7 $198.44   9.850%   $217.9863   $217.99   $218.00   $218.00  
  7 purchase totals = $820.74       $901.9333   $901.94   $901.95   $901.90