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 $165.58   10.506%   $182.9758   $182.98   $183.00   $183.00  
  Purchase #2 $207.81   11.330%   $231.3549   $231.35   $231.35   $231.40  
  Purchase #3 $113.62   12.732%   $128.0861   $128.09   $128.10   $128.10  
  Purchase #4 $168.89   3.728%   $175.1862   $175.19   $175.20   $175.20  
  Purchase #5 $15.80   7.218%   $16.9404   $16.94   $16.95   $16.90  
  Purchase #6 $43.71   8.742%   $47.5311   $47.53   $47.55   $47.50  
  Purchase #7 $203.73   11.603%   $227.3688   $227.37   $227.35   $227.40  
  7 purchase totals = $919.14       $1,009.4433   $1,009.45   $1,009.50   $1,009.50