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 $203.92   12.635%   $229.6853   $229.69   $229.70   $229.70  
  Purchase #2 $151.25   8.351%   $163.8809   $163.88   $163.90   $163.90  
  Purchase #3 $102.67   13.690%   $116.7255   $116.73   $116.75   $116.70  
  Purchase #4 $95.68   4.397%   $99.887   $99.89   $99.90   $99.90  
  Purchase #5 $130.33   7.252%   $139.7815   $139.78   $139.80   $139.80  
  Purchase #6 $111.97   13.752%   $127.3681   $127.37   $127.35   $127.40  
  Purchase #7 $177.44   3.329%   $183.347   $183.35   $183.35   $183.30  
  7 purchase totals = $973.26       $1,060.6753   $1,060.69   $1,060.75   $1,060.70