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 $228.65   6.393%   $243.2676   $243.27   $243.25   $243.30  
  Purchase #2 $86.37   9.525%   $94.5967   $94.60   $94.60   $94.60  
  Purchase #3 $198.73   7.684%   $214.0004   $214.00   $214.00   $214.00  
  Purchase #4 $189.51   4.769%   $198.5477   $198.55   $198.55   $198.50  
  Purchase #5 $197.99   3.756%   $205.4265   $205.43   $205.45   $205.40  
  Purchase #6 $91.49   3.325%   $94.532   $94.53   $94.55   $94.50  
  Purchase #7 $128.56   11.874%   $143.8252   $143.83   $143.85   $143.80  
  7 purchase totals = $1,121.30       $1,194.1961   $1,194.21   $1,194.25   $1,194.10