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 $58.76   5.383%   $61.9231   $61.92   $61.90   $61.90  
  Purchase #2 $199.46   6.381%   $212.1875   $212.19   $212.20   $212.20  
  Purchase #3 $130.46   7.253%   $139.9223   $139.92   $139.90   $139.90  
  Purchase #4 $193.25   9.667%   $211.9315   $211.93   $211.95   $211.90  
  Purchase #5 $11.77   7.369%   $12.6373   $12.64   $12.65   $12.60  
  Purchase #6 $84.90   9.201%   $92.7116   $92.71   $92.70   $92.70  
  Purchase #7 $29.73   11.172%   $33.0514   $33.05   $33.05   $33.10  
  7 purchase totals = $708.33       $764.3647   $764.36   $764.35   $764.30