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 $196.49   6.113%   $208.5014   $208.50   $208.50   $208.50  
  Purchase #2 $50.54   3.748%   $52.4342   $52.43   $52.45   $52.40  
  Purchase #3 $167.83   12.120%   $188.171   $188.17   $188.15   $188.20  
  Purchase #4 $243.41   8.260%   $263.5157   $263.52   $263.50   $263.50  
  Purchase #5 $94.55   7.774%   $101.9003   $101.90   $101.90   $101.90  
  Purchase #6 $118.73   9.356%   $129.8384   $129.84   $129.85   $129.80  
  Purchase #7 $239.63   12.530%   $269.6556   $269.66   $269.65   $269.70  
  7 purchase totals = $1,111.18       $1,214.0166   $1,214.02   $1,214.00   $1,214.00