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 $159.52   7.261%   $171.1027   $171.10   $171.10   $171.10  
  Purchase #2 $212.65   4.631%   $222.4978   $222.50   $222.50   $222.50  
  Purchase #3 $102.80   11.449%   $114.5696   $114.57   $114.55   $114.60  
  Purchase #4 $64.84   8.776%   $70.5304   $70.53   $70.55   $70.50  
  Purchase #5 $211.73   10.475%   $233.9087   $233.91   $233.90   $233.90  
  Purchase #6 $116.86   6.277%   $124.1953   $124.20   $124.20   $124.20  
  Purchase #7 $185.26   7.318%   $198.8173   $198.82   $198.80   $198.80  
  7 purchase totals = $1,053.66       $1,135.6218   $1,135.63   $1,135.60   $1,135.60