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 $222.94   13.768%   $253.6344   $253.63   $253.65   $253.60  
  Purchase #2 $116.37   8.662%   $126.45   $126.45   $126.45   $126.50  
  Purchase #3 $34.93   3.677%   $36.2144   $36.21   $36.20   $36.20  
  Purchase #4 $199.52   3.263%   $206.0303   $206.03   $206.05   $206.00  
  Purchase #5 $209.49   3.242%   $216.2817   $216.28   $216.30   $216.30  
  Purchase #6 $201.29   4.824%   $211.0002   $211.00   $211.00   $211.00  
  Purchase #7 $222.90   13.335%   $252.6237   $252.62   $252.60   $252.60  
  7 purchase totals = $1,207.44       $1,302.2347   $1,302.22   $1,302.25   $1,302.20