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 $219.47   11.131%   $243.8992   $243.90   $243.90   $243.90  
  Purchase #2 $160.27   10.775%   $177.5391   $177.54   $177.55   $177.50  
  Purchase #3 $70.55   10.779%   $78.1546   $78.15   $78.15   $78.20  
  Purchase #4 $177.65   13.362%   $201.3876   $201.39   $201.40   $201.40  
  Purchase #5 $206.58   3.650%   $214.1202   $214.12   $214.10   $214.10  
  Purchase #6 $213.85   8.150%   $231.2788   $231.28   $231.30   $231.30  
  Purchase #7 $79.28   11.267%   $88.2125   $88.21   $88.20   $88.20  
  7 purchase totals = $1,127.65       $1,234.5920   $1,234.59   $1,234.60   $1,234.60