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 $245.35   12.643%   $276.3696   $276.37   $276.35   $276.40  
  Purchase #2 $22.50   8.686%   $24.4544   $24.45   $24.45   $24.50  
  Purchase #3 $162.28   5.321%   $170.9149   $170.91   $170.90   $170.90  
  Purchase #4 $228.97   12.849%   $258.3904   $258.39   $258.40   $258.40  
  Purchase #5 $184.27   9.116%   $201.0681   $201.07   $201.05   $201.10  
  Purchase #6 $214.50   6.636%   $228.7342   $228.73   $228.75   $228.70  
  Purchase #7 $203.60   7.221%   $218.302   $218.30   $218.30   $218.30  
  7 purchase totals = $1,261.47       $1,378.2336   $1,378.22   $1,378.20   $1,378.30