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 $58.57   13.860%   $66.6878   $66.69   $66.70   $66.70  
  Purchase #2 $210.94   10.484%   $233.0549   $233.05   $233.05   $233.10  
  Purchase #3 $160.68   13.204%   $181.8962   $181.90   $181.90   $181.90  
  Purchase #4 $190.82   12.483%   $214.6401   $214.64   $214.65   $214.60  
  Purchase #5 $135.73   7.226%   $145.5378   $145.54   $145.55   $145.50  
  Purchase #6 $193.43   10.220%   $213.1985   $213.20   $213.20   $213.20  
  Purchase #7 $31.54   10.801%   $34.9466   $34.95   $34.95   $34.90  
  7 purchase totals = $981.71       $1,089.9619   $1,089.97   $1,090.00   $1,089.90