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 $88.70   5.464%   $93.5466   $93.55   $93.55   $93.50  
  Purchase #2 $237.74   13.426%   $269.659   $269.66   $269.65   $269.70  
  Purchase #3 $28.55   7.261%   $30.623   $30.62   $30.60   $30.60  
  Purchase #4 $241.93   10.318%   $266.8923   $266.89   $266.90   $266.90  
  Purchase #5 $130.59   7.307%   $140.1322   $140.13   $140.15   $140.10  
  Purchase #6 $219.37   3.827%   $227.7653   $227.77   $227.75   $227.80  
  Purchase #7 $239.86   5.495%   $253.0403   $253.04   $253.05   $253.00  
  7 purchase totals = $1,186.74       $1,281.6587   $1,281.66   $1,281.65   $1,281.60