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 $126.29   9.755%   $138.6096   $138.61   $138.60   $138.60  
  Purchase #2 $199.73   3.516%   $206.7525   $206.75   $206.75   $206.80  
  Purchase #3 $239.83   12.674%   $270.2261   $270.23   $270.25   $270.20  
  Purchase #4 $181.26   5.325%   $190.9121   $190.91   $190.90   $190.90  
  Purchase #5 $55.84   13.823%   $63.5588   $63.56   $63.55   $63.60  
  Purchase #6 $155.85   13.819%   $177.3869   $177.39   $177.40   $177.40  
  Purchase #7 $188.99   6.770%   $201.7846   $201.78   $201.80   $201.80  
  7 purchase totals = $1,147.79       $1,249.2306   $1,249.23   $1,249.25   $1,249.30