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 $83.31   4.711%   $87.2347   $87.23   $87.25   $87.20  
  Purchase #2 $58.94   9.338%   $64.4438   $64.44   $64.45   $64.40  
  Purchase #3 $231.31   10.829%   $256.3586   $256.36   $256.35   $256.40  
  Purchase #4 $187.46   5.798%   $198.3289   $198.33   $198.35   $198.30  
  Purchase #5 $74.53   7.559%   $80.1637   $80.16   $80.15   $80.20  
  Purchase #6 $99.87   3.416%   $103.2816   $103.28   $103.30   $103.30  
  Purchase #7 $89.28   10.440%   $98.6008   $98.60   $98.60   $98.60  
  7 purchase totals = $824.70       $888.4121   $888.40   $888.45   $888.40