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 $232.85   12.536%   $262.0401   $262.04   $262.05   $262.00  
  Purchase #2 $127.29   4.201%   $132.6375   $132.64   $132.65   $132.60  
  Purchase #3 $89.96   8.163%   $97.3034   $97.30   $97.30   $97.30  
  Purchase #4 $191.80   12.775%   $216.3025   $216.30   $216.30   $216.30  
  Purchase #5 $108.81   11.230%   $121.0294   $121.03   $121.05   $121.00  
  Purchase #6 $227.63   13.853%   $259.1636   $259.16   $259.15   $259.20  
  Purchase #7 $53.65   6.455%   $57.1131   $57.11   $57.10   $57.10  
  7 purchase totals = $1,031.99       $1,145.5896   $1,145.58   $1,145.60   $1,145.50