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 $192.54   11.588%   $214.8515   $214.85   $214.85   $214.90  
  Purchase #2 $124.76   13.766%   $141.9345   $141.93   $141.95   $141.90  
  Purchase #3 $204.27   9.719%   $224.123   $224.12   $224.10   $224.10  
  Purchase #4 $58.58   10.229%   $64.5721   $64.57   $64.55   $64.60  
  Purchase #5 $63.49   5.832%   $67.1927   $67.19   $67.20   $67.20  
  Purchase #6 $225.44   3.135%   $232.5075   $232.51   $232.50   $232.50  
  Purchase #7 $69.32   13.598%   $78.7461   $78.75   $78.75   $78.70  
  7 purchase totals = $938.40       $1,023.9274   $1,023.92   $1,023.90   $1,023.90