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 $198.25   11.619%   $221.2847   $221.28   $221.30   $221.30  
  Purchase #2 $95.29   12.257%   $106.9697   $106.97   $106.95   $107.00  
  Purchase #3 $39.43   8.450%   $42.7618   $42.76   $42.75   $42.80  
  Purchase #4 $231.88   5.608%   $244.8838   $244.88   $244.90   $244.90  
  Purchase #5 $207.51   12.862%   $234.1999   $234.20   $234.20   $234.20  
  Purchase #6 $94.38   9.572%   $103.4141   $103.41   $103.40   $103.40  
  Purchase #7 $183.50   12.791%   $206.9715   $206.97   $206.95   $207.00  
  7 purchase totals = $1,050.24       $1,160.4855   $1,160.47   $1,160.45   $1,160.60