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 $97.28   8.612%   $105.6578   $105.66   $105.65   $105.70  
  Purchase #2 $222.70   5.204%   $234.2893   $234.29   $234.30   $234.30  
  Purchase #3 $144.56   8.569%   $156.9473   $156.95   $156.95   $156.90  
  Purchase #4 $25.54   8.797%   $27.7868   $27.79   $27.80   $27.80  
  Purchase #5 $154.66   7.673%   $166.5271   $166.53   $166.55   $166.50  
  Purchase #6 $58.70   3.445%   $60.7222   $60.72   $60.70   $60.70  
  Purchase #7 $204.78   6.395%   $217.8757   $217.88   $217.90   $217.90  
  7 purchase totals = $908.22       $969.8062   $969.82   $969.85   $969.80