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 $196.28   8.822%   $213.5958   $213.60   $213.60   $213.60  
  Purchase #2 $124.85   13.728%   $141.9894   $141.99   $142.00   $142.00  
  Purchase #3 $232.99   7.716%   $250.9675   $250.97   $250.95   $251.00  
  Purchase #4 $33.25   6.814%   $35.5157   $35.52   $35.50   $35.50  
  Purchase #5 $119.56   12.578%   $134.5983   $134.60   $134.60   $134.60  
  Purchase #6 $64.35   6.372%   $68.4504   $68.45   $68.45   $68.50  
  Purchase #7 $96.96   12.686%   $109.2603   $109.26   $109.25   $109.30  
  7 purchase totals = $868.24       $954.3774   $954.39   $954.35   $954.50