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 $198.80   11.631%   $221.9224   $221.92   $221.90   $221.90  
  Purchase #2 $80.47   13.226%   $91.113   $91.11   $91.10   $91.10  
  Purchase #3 $150.69   11.461%   $167.9606   $167.96   $167.95   $168.00  
  Purchase #4 $222.46   4.748%   $233.0224   $233.02   $233.00   $233.00  
  Purchase #5 $188.95   7.548%   $203.2119   $203.21   $203.20   $203.20  
  Purchase #6 $166.41   7.353%   $178.6461   $178.65   $178.65   $178.60  
  Purchase #7 $61.59   10.143%   $67.8371   $67.84   $67.85   $67.80  
  7 purchase totals = $1,069.37       $1,163.7135   $1,163.71   $1,163.65   $1,163.60