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 $212.63   13.171%   $240.6355   $240.64   $240.65   $240.60  
  Purchase #2 $185.26   4.520%   $193.6338   $193.63   $193.65   $193.60  
  Purchase #3 $97.33   10.394%   $107.4465   $107.45   $107.45   $107.40  
  Purchase #4 $222.80   13.623%   $253.152   $253.15   $253.15   $253.20  
  Purchase #5 $34.95   3.387%   $36.1338   $36.13   $36.15   $36.10  
  Purchase #6 $246.92   11.495%   $275.3035   $275.30   $275.30   $275.30  
  Purchase #7 $91.25   5.584%   $96.3454   $96.35   $96.35   $96.30  
  7 purchase totals = $1,091.14       $1,202.6505   $1,202.65   $1,202.70   $1,202.50