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 $64.84   10.233%   $71.4751   $71.48   $71.50   $71.50  
  Purchase #2 $65.61   12.864%   $74.0501   $74.05   $74.05   $74.10  
  Purchase #3 $248.73   7.156%   $266.5291   $266.53   $266.55   $266.50  
  Purchase #4 $110.78   8.596%   $120.3026   $120.30   $120.30   $120.30  
  Purchase #5 $170.47   7.346%   $182.9927   $182.99   $183.00   $183.00  
  Purchase #6 $232.34   8.563%   $252.2353   $252.24   $252.25   $252.20  
  Purchase #7 $100.47   8.203%   $108.7116   $108.71   $108.70   $108.70  
  7 purchase totals = $993.24       $1,076.2965   $1,076.30   $1,076.35   $1,076.30