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 $60.78   5.667%   $64.2244   $64.22   $64.20   $64.20  
  Purchase #2 $215.46   12.537%   $242.4722   $242.47   $242.45   $242.50  
  Purchase #3 $220.84   8.524%   $239.6644   $239.66   $239.65   $239.70  
  Purchase #4 $210.73   7.218%   $225.9405   $225.94   $225.95   $225.90  
  Purchase #5 $69.54   9.290%   $76.0003   $76.00   $76.00   $76.00  
  Purchase #6 $74.85   8.601%   $81.2878   $81.29   $81.30   $81.30  
  Purchase #7 $85.66   13.194%   $96.962   $96.96   $96.95   $97.00  
  7 purchase totals = $937.86       $1,026.5516   $1,026.54   $1,026.50   $1,026.60