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 $236.64   11.264%   $263.2951   $263.30   $263.30   $263.30  
  Purchase #2 $172.97   7.283%   $185.5674   $185.57   $185.55   $185.60  
  Purchase #3 $203.34   9.790%   $223.247   $223.25   $223.25   $223.20  
  Purchase #4 $204.64   11.837%   $228.8632   $228.86   $228.85   $228.90  
  Purchase #5 $58.49   12.213%   $65.6334   $65.63   $65.65   $65.60  
  Purchase #6 $184.29   4.462%   $192.513   $192.51   $192.50   $192.50  
  Purchase #7 $135.32   6.318%   $143.8695   $143.87   $143.85   $143.90  
  7 purchase totals = $1,195.69       $1,302.9886   $1,302.99   $1,302.95   $1,303.00