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 $196.52   5.160%   $206.6604   $206.66   $206.65   $206.70  
  Purchase #2 $233.99   10.292%   $258.0723   $258.07   $258.05   $258.10  
  Purchase #3 $67.29   10.314%   $74.2303   $74.23   $74.25   $74.20  
  Purchase #4 $45.67   8.614%   $49.604   $49.60   $49.60   $49.60  
  Purchase #5 $238.79   12.186%   $267.8889   $267.89   $267.90   $267.90  
  Purchase #6 $228.92   9.199%   $249.9784   $249.98   $250.00   $250.00  
  Purchase #7 $128.47   6.653%   $137.0171   $137.02   $137.00   $137.00  
  7 purchase totals = $1,139.65       $1,243.4514   $1,243.45   $1,243.45   $1,243.50