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 $164.98   11.679%   $184.248   $184.25   $184.25   $184.20  
  Purchase #2 $77.80   7.640%   $83.7439   $83.74   $83.75   $83.70  
  Purchase #3 $16.70   11.382%   $18.6008   $18.60   $18.60   $18.60  
  Purchase #4 $23.64   10.163%   $26.0425   $26.04   $26.05   $26.00  
  Purchase #5 $206.43   4.304%   $215.3147   $215.31   $215.30   $215.30  
  Purchase #6 $103.44   3.182%   $106.7315   $106.73   $106.75   $106.70  
  Purchase #7 $218.53   13.106%   $247.1705   $247.17   $247.15   $247.20  
  7 purchase totals = $811.52       $881.8519   $881.84   $881.85   $881.70