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 $116.30   13.507%   $132.0086   $132.01   $132.00   $132.00  
  Purchase #2 $222.77   7.144%   $238.6847   $238.68   $238.70   $238.70  
  Purchase #3 $56.83   7.162%   $60.9002   $60.90   $60.90   $60.90  
  Purchase #4 $175.78   4.547%   $183.7727   $183.77   $183.75   $183.80  
  Purchase #5 $197.75   12.712%   $222.888   $222.89   $222.90   $222.90  
  Purchase #6 $176.94   12.209%   $198.5426   $198.54   $198.55   $198.50  
  Purchase #7 $82.74   13.193%   $93.6559   $93.66   $93.65   $93.70  
  7 purchase totals = $1,029.11       $1,130.4527   $1,130.45   $1,130.45   $1,130.50