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 $164.67   10.339%   $181.6952   $181.70   $181.70   $181.70  
  Purchase #2 $187.63   10.146%   $206.6669   $206.67   $206.65   $206.70  
  Purchase #3 $180.53   5.611%   $190.6595   $190.66   $190.65   $190.70  
  Purchase #4 $230.99   6.631%   $246.3069   $246.31   $246.30   $246.30  
  Purchase #5 $56.65   9.450%   $62.0034   $62.00   $62.00   $62.00  
  Purchase #6 $54.51   3.842%   $56.6043   $56.60   $56.60   $56.60  
  Purchase #7 $44.44   9.654%   $48.7302   $48.73   $48.75   $48.70  
  7 purchase totals = $919.42       $992.6664   $992.67   $992.65   $992.70