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 $34.59   6.534%   $36.8501   $36.85   $36.85   $36.90  
  Purchase #2 $215.81   10.825%   $239.1714   $239.17   $239.15   $239.20  
  Purchase #3 $123.47   9.324%   $134.9823   $134.98   $135.00   $135.00  
  Purchase #4 $155.28   7.111%   $166.322   $166.32   $166.30   $166.30  
  Purchase #5 $54.35   8.630%   $59.0404   $59.04   $59.05   $59.00  
  Purchase #6 $233.57   4.460%   $243.9872   $243.99   $244.00   $244.00  
  Purchase #7 $63.50   11.729%   $70.9479   $70.95   $70.95   $70.90  
  7 purchase totals = $880.57       $951.3013   $951.30   $951.30   $951.30