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 $217.58   11.757%   $243.1609   $243.16   $243.15   $243.20  
  Purchase #2 $49.37   11.700%   $55.1463   $55.15   $55.15   $55.10  
  Purchase #3 $103.42   9.835%   $113.5914   $113.59   $113.60   $113.60  
  Purchase #4 $73.45   3.524%   $76.0384   $76.04   $76.05   $76.00  
  Purchase #5 $141.49   4.243%   $147.4934   $147.49   $147.50   $147.50  
  Purchase #6 $248.95   10.847%   $275.9536   $275.95   $275.95   $276.00  
  Purchase #7 $207.40   5.695%   $219.2114   $219.21   $219.20   $219.20  
  7 purchase totals = $1,041.66       $1,130.5954   $1,130.59   $1,130.60   $1,130.60