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 $50.77   10.693%   $56.1988   $56.20   $56.20   $56.20  
  Purchase #2 $158.48   5.303%   $166.8842   $166.88   $166.90   $166.90  
  Purchase #3 $246.65   12.745%   $278.0855   $278.09   $278.10   $278.10  
  Purchase #4 $44.92   6.485%   $47.8331   $47.83   $47.85   $47.80  
  Purchase #5 $176.70   11.486%   $196.9958   $197.00   $197.00   $197.00  
  Purchase #6 $90.44   5.627%   $95.5291   $95.53   $95.55   $95.50  
  Purchase #7 $199.36   3.392%   $206.1223   $206.12   $206.10   $206.10  
  7 purchase totals = $967.32       $1,047.6488   $1,047.65   $1,047.70   $1,047.60