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 $173.33   9.761%   $190.2487   $190.25   $190.25   $190.20  
  Purchase #2 $159.41   3.248%   $164.5876   $164.59   $164.60   $164.60  
  Purchase #3 $233.87   3.222%   $241.4053   $241.41   $241.40   $241.40  
  Purchase #4 $207.78   12.727%   $234.2242   $234.22   $234.20   $234.20  
  Purchase #5 $94.53   11.654%   $105.5465   $105.55   $105.55   $105.50  
  Purchase #6 $225.91   9.218%   $246.7344   $246.73   $246.75   $246.70  
  Purchase #7 $75.62   4.641%   $79.1295   $79.13   $79.15   $79.10  
  7 purchase totals = $1,170.45       $1,261.8762   $1,261.88   $1,261.90   $1,261.70