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 $100.49   3.617%   $104.1247   $104.12   $104.10   $104.10  
  Purchase #2 $23.80   6.769%   $25.411   $25.41   $25.40   $25.40  
  Purchase #3 $247.69   12.685%   $279.1095   $279.11   $279.10   $279.10  
  Purchase #4 $120.74   8.256%   $130.7083   $130.71   $130.70   $130.70  
  Purchase #5 $98.72   7.803%   $106.4231   $106.42   $106.40   $106.40  
  Purchase #6 $232.84   10.836%   $258.0705   $258.07   $258.05   $258.10  
  Purchase #7 $180.64   13.870%   $205.6948   $205.69   $205.70   $205.70  
  7 purchase totals = $1,004.92       $1,109.5419   $1,109.53   $1,109.45   $1,109.50