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 $235.88   9.713%   $258.791   $258.79   $258.80   $258.80  
  Purchase #2 $172.40   5.131%   $181.2458   $181.25   $181.25   $181.20  
  Purchase #3 $95.48   11.414%   $106.3781   $106.38   $106.40   $106.40  
  Purchase #4 $125.73   9.176%   $137.267   $137.27   $137.25   $137.30  
  Purchase #5 $63.85   7.798%   $68.829   $68.83   $68.85   $68.80  
  Purchase #6 $157.43   11.629%   $175.7375   $175.74   $175.75   $175.70  
  Purchase #7 $247.85   3.625%   $256.8346   $256.83   $256.85   $256.80  
  7 purchase totals = $1,098.62       $1,185.0830   $1,185.09   $1,185.15   $1,185.00