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 $5.29   9.109%   $5.7719   $5.77   $5.75   $5.80  
  Purchase #2 $244.54   8.450%   $265.2036   $265.20   $265.20   $265.20  
  Purchase #3 $165.96   5.677%   $175.3815   $175.38   $175.40   $175.40  
  Purchase #4 $32.72   4.341%   $34.1404   $34.14   $34.15   $34.10  
  Purchase #5 $204.57   3.835%   $212.4153   $212.42   $212.40   $212.40  
  Purchase #6 $242.74   13.729%   $276.0658   $276.07   $276.05   $276.10  
  Purchase #7 $95.97   4.498%   $100.2867   $100.29   $100.30   $100.30  
  7 purchase totals = $991.79       $1,069.2652   $1,069.27   $1,069.25   $1,069.30