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 $90.77   6.720%   $96.8697   $96.87   $96.85   $96.90  
  Purchase #2 $211.70   6.488%   $225.4351   $225.44   $225.45   $225.40  
  Purchase #3 $136.48   6.407%   $145.2243   $145.22   $145.20   $145.20  
  Purchase #4 $34.69   4.265%   $36.1695   $36.17   $36.15   $36.20  
  Purchase #5 $187.50   8.622%   $203.6663   $203.67   $203.65   $203.70  
  Purchase #6 $165.53   10.206%   $182.424   $182.42   $182.40   $182.40  
  Purchase #7 $29.95   12.691%   $33.751   $33.75   $33.75   $33.80  
  7 purchase totals = $856.62       $923.5399   $923.54   $923.45   $923.60