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 $196.99   8.552%   $213.8366   $213.84   $213.85   $213.80  
  Purchase #2 $163.94   13.134%   $185.4719   $185.47   $185.45   $185.50  
  Purchase #3 $224.93   10.367%   $248.2485   $248.25   $248.25   $248.20  
  Purchase #4 $96.57   13.744%   $109.8426   $109.84   $109.85   $109.80  
  Purchase #5 $67.52   11.807%   $75.4921   $75.49   $75.50   $75.50  
  Purchase #6 $102.70   5.451%   $108.2982   $108.30   $108.30   $108.30  
  Purchase #7 $26.37   6.639%   $28.1207   $28.12   $28.10   $28.10  
  7 purchase totals = $879.02       $969.3106   $969.31   $969.30   $969.20