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 $154.65   5.791%   $163.6058   $163.61   $163.60   $163.60  
  Purchase #2 $40.53   11.642%   $45.2485   $45.25   $45.25   $45.20  
  Purchase #3 $23.77   9.631%   $26.0593   $26.06   $26.05   $26.10  
  Purchase #4 $184.58   7.372%   $198.1872   $198.19   $198.20   $198.20  
  Purchase #5 $63.63   3.409%   $65.7991   $65.80   $65.80   $65.80  
  Purchase #6 $200.51   12.353%   $225.279   $225.28   $225.30   $225.30  
  Purchase #7 $85.50   10.176%   $94.2005   $94.20   $94.20   $94.20  
  7 purchase totals = $753.17       $818.3794   $818.39   $818.40   $818.40