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 $93.63   9.156%   $102.2028   $102.20   $102.20   $102.20  
  Purchase #2 $186.66   12.325%   $209.6658   $209.67   $209.65   $209.70  
  Purchase #3 $130.42   7.851%   $140.6593   $140.66   $140.65   $140.70  
  Purchase #4 $244.43   6.212%   $259.614   $259.61   $259.60   $259.60  
  Purchase #5 $107.53   5.867%   $113.8388   $113.84   $113.85   $113.80  
  Purchase #6 $225.45   3.219%   $232.7072   $232.71   $232.70   $232.70  
  Purchase #7 $243.99   9.276%   $266.6225   $266.62   $266.60   $266.60  
  7 purchase totals = $1,232.11       $1,325.3104   $1,325.31   $1,325.25   $1,325.30