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 $168.47   11.191%   $187.3235   $187.32   $187.30   $187.30  
  Purchase #2 $189.49   4.598%   $198.2028   $198.20   $198.20   $198.20  
  Purchase #3 $9.48   4.687%   $9.9243   $9.92   $9.90   $9.90  
  Purchase #4 $222.76   10.370%   $245.8602   $245.86   $245.85   $245.90  
  Purchase #5 $111.97   11.521%   $124.8701   $124.87   $124.85   $124.90  
  Purchase #6 $204.74   9.871%   $224.9499   $224.95   $224.95   $224.90  
  Purchase #7 $37.62   3.261%   $38.8468   $38.85   $38.85   $38.80  
  7 purchase totals = $944.53       $1,029.9776   $1,029.97   $1,029.90   $1,029.90