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 $124.46   13.871%   $141.7238   $141.72   $141.70   $141.70  
  Purchase #2 $177.94   3.524%   $184.2106   $184.21   $184.20   $184.20  
  Purchase #3 $63.42   11.530%   $70.7323   $70.73   $70.75   $70.70  
  Purchase #4 $192.97   12.319%   $216.742   $216.74   $216.75   $216.70  
  Purchase #5 $114.32   11.286%   $127.2222   $127.22   $127.20   $127.20  
  Purchase #6 $237.71   6.598%   $253.3941   $253.39   $253.40   $253.40  
  Purchase #7 $241.37   12.728%   $272.0916   $272.09   $272.10   $272.10  
  7 purchase totals = $1,152.19       $1,266.1166   $1,266.10   $1,266.10   $1,266.00