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 $207.54   11.426%   $231.2535   $231.25   $231.25   $231.30  
  Purchase #2 $185.53   5.107%   $195.005   $195.01   $195.00   $195.00  
  Purchase #3 $155.56   12.845%   $175.5417   $175.54   $175.55   $175.50  
  Purchase #4 $60.30   6.560%   $64.2557   $64.26   $64.25   $64.30  
  Purchase #5 $113.39   5.102%   $119.1752   $119.18   $119.20   $119.20  
  Purchase #6 $250.88   13.783%   $285.4588   $285.46   $285.45   $285.50  
  Purchase #7 $147.62   4.803%   $154.7102   $154.71   $154.70   $154.70  
  7 purchase totals = $1,120.82       $1,225.4001   $1,225.41   $1,225.40   $1,225.50