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 $94.73   5.463%   $99.9051   $99.91   $99.90   $99.90  
  Purchase #2 $196.82   5.143%   $206.9425   $206.94   $206.95   $206.90  
  Purchase #3 $192.96   11.669%   $215.4765   $215.48   $215.50   $215.50  
  Purchase #4 $186.54   8.648%   $202.672   $202.67   $202.65   $202.70  
  Purchase #5 $237.83   12.260%   $266.988   $266.99   $267.00   $267.00  
  Purchase #6 $147.32   8.432%   $159.742   $159.74   $159.75   $159.70  
  Purchase #7 $178.88   10.736%   $198.0846   $198.08   $198.10   $198.10  
  7 purchase totals = $1,235.08       $1,349.8107   $1,349.81   $1,349.85   $1,349.80