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 $166.54   7.292%   $178.6841   $178.68   $178.70   $178.70  
  Purchase #2 $31.45   12.316%   $35.3234   $35.32   $35.30   $35.30  
  Purchase #3 $51.35   8.869%   $55.9042   $55.90   $55.90   $55.90  
  Purchase #4 $22.94   4.451%   $23.9611   $23.96   $23.95   $24.00  
  Purchase #5 $205.79   5.505%   $217.1187   $217.12   $217.10   $217.10  
  Purchase #6 $6.97   10.424%   $7.6966   $7.70   $7.70   $7.70  
  Purchase #7 $17.86   11.316%   $19.881   $19.88   $19.90   $19.90  
  7 purchase totals = $502.90       $538.5691   $538.56   $538.55   $538.60