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 $108.49   10.319%   $119.6851   $119.69   $119.70   $119.70  
  Purchase #2 $239.94   3.323%   $247.9132   $247.91   $247.90   $247.90  
  Purchase #3 $216.49   3.494%   $224.0542   $224.05   $224.05   $224.10  
  Purchase #4 $29.95   4.651%   $31.343   $31.34   $31.35   $31.30  
  Purchase #5 $104.51   13.791%   $118.923   $118.92   $118.90   $118.90  
  Purchase #6 $153.92   12.691%   $173.454   $173.45   $173.45   $173.50  
  Purchase #7 $156.49   4.641%   $163.7527   $163.75   $163.75   $163.80  
  7 purchase totals = $1,009.79       $1,079.1252   $1,079.11   $1,079.10   $1,079.20