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 $61.88   3.440%   $64.0087   $64.01   $64.00   $64.00  
  Purchase #2 $13.75   5.257%   $14.4728   $14.47   $14.45   $14.50  
  Purchase #3 $185.78   9.183%   $202.8402   $202.84   $202.85   $202.80  
  Purchase #4 $218.59   6.742%   $233.3273   $233.33   $233.35   $233.30  
  Purchase #5 $189.81   13.867%   $216.131   $216.13   $216.15   $216.10  
  Purchase #6 $167.53   9.695%   $183.772   $183.77   $183.75   $183.80  
  Purchase #7 $108.64   4.752%   $113.8026   $113.80   $113.80   $113.80  
  7 purchase totals = $945.98       $1,028.3546   $1,028.35   $1,028.35   $1,028.30