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 $84.51   13.560%   $95.9696   $95.97   $95.95   $96.00  
  Purchase #2 $141.46   3.488%   $146.3941   $146.39   $146.40   $146.40  
  Purchase #3 $61.77   5.652%   $65.2612   $65.26   $65.25   $65.30  
  Purchase #4 $214.74   11.303%   $239.0121   $239.01   $239.00   $239.00  
  Purchase #5 $173.74   4.753%   $181.9979   $182.00   $182.00   $182.00  
  Purchase #6 $74.25   12.817%   $83.7666   $83.77   $83.75   $83.80  
  Purchase #7 $192.40   13.706%   $218.7703   $218.77   $218.75   $218.80  
  7 purchase totals = $942.87       $1,031.1718   $1,031.17   $1,031.10   $1,031.30