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 $193.71   6.327%   $205.966   $205.97   $205.95   $206.00  
  Purchase #2 $113.87   3.823%   $118.2233   $118.22   $118.20   $118.20  
  Purchase #3 $240.73   3.108%   $248.2119   $248.21   $248.20   $248.20  
  Purchase #4 $51.27   7.554%   $55.1429   $55.14   $55.15   $55.10  
  Purchase #5 $145.34   3.815%   $150.8847   $150.88   $150.90   $150.90  
  Purchase #6 $61.48   3.644%   $63.7203   $63.72   $63.70   $63.70  
  Purchase #7 $184.73   11.744%   $206.4247   $206.42   $206.40   $206.40  
  7 purchase totals = $991.13       $1,048.5738   $1,048.56   $1,048.50   $1,048.50