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 $73.71   13.377%   $83.5702   $83.57   $83.55   $83.60  
  Purchase #2 $56.53   7.273%   $60.6414   $60.64   $60.65   $60.60  
  Purchase #3 $201.64   6.412%   $214.5692   $214.57   $214.55   $214.60  
  Purchase #4 $95.69   9.577%   $104.8542   $104.85   $104.85   $104.90  
  Purchase #5 $196.94   12.487%   $221.5319   $221.53   $221.55   $221.50  
  Purchase #6 $156.94   8.835%   $170.8056   $170.81   $170.80   $170.80  
  Purchase #7 $158.80   11.795%   $177.5305   $177.53   $177.55   $177.50  
  7 purchase totals = $940.25       $1,033.5030   $1,033.50   $1,033.50   $1,033.50