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 $163.71   12.564%   $184.2785   $184.28   $184.30   $184.30  
  Purchase #2 $52.42   7.197%   $56.1927   $56.19   $56.20   $56.20  
  Purchase #3 $66.34   10.813%   $73.5133   $73.51   $73.50   $73.50  
  Purchase #4 $95.90   10.807%   $106.2639   $106.26   $106.25   $106.30  
  Purchase #5 $221.61   7.773%   $238.8357   $238.84   $238.85   $238.80  
  Purchase #6 $227.85   13.137%   $257.7827   $257.78   $257.80   $257.80  
  Purchase #7 $180.78   6.375%   $192.3047   $192.30   $192.30   $192.30  
  7 purchase totals = $1,008.61       $1,109.1715   $1,109.16   $1,109.20   $1,109.20