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 $174.35   13.479%   $197.8506   $197.85   $197.85   $197.90  
  Purchase #2 $152.61   3.122%   $157.3745   $157.37   $157.35   $157.40  
  Purchase #3 $145.65   12.359%   $163.6509   $163.65   $163.65   $163.70  
  Purchase #4 $189.46   7.817%   $204.2701   $204.27   $204.25   $204.30  
  Purchase #5 $48.37   6.823%   $51.6703   $51.67   $51.65   $51.70  
  Purchase #6 $116.64   9.271%   $127.4537   $127.45   $127.45   $127.50  
  Purchase #7 $60.60   11.260%   $67.4236   $67.42   $67.40   $67.40  
  7 purchase totals = $887.68       $969.6937   $969.68   $969.60   $969.90