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 $233.97   3.261%   $241.5998   $241.60   $241.60   $241.60  
  Purchase #2 $136.31   11.489%   $151.9707   $151.97   $151.95   $152.00  
  Purchase #3 $58.78   12.622%   $66.1992   $66.20   $66.20   $66.20  
  Purchase #4 $231.87   8.563%   $251.725   $251.73   $251.75   $251.70  
  Purchase #5 $53.37   6.776%   $56.9864   $56.99   $57.00   $57.00  
  Purchase #6 $39.33   7.719%   $42.3659   $42.37   $42.35   $42.40  
  Purchase #7 $45.28   11.170%   $50.3378   $50.34   $50.35   $50.30  
  7 purchase totals = $798.91       $861.1848   $861.20   $861.20   $861.20