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 $242.70   7.156%   $260.0676   $260.07   $260.05   $260.10  
  Purchase #2 $68.31   6.779%   $72.9407   $72.94   $72.95   $72.90  
  Purchase #3 $118.68   8.764%   $129.0811   $129.08   $129.10   $129.10  
  Purchase #4 $55.89   9.453%   $61.1733   $61.17   $61.15   $61.20  
  Purchase #5 $196.97   6.227%   $209.2353   $209.24   $209.25   $209.20  
  Purchase #6 $189.29   12.616%   $213.1708   $213.17   $213.15   $213.20  
  Purchase #7 $181.70   12.238%   $203.9364   $203.94   $203.95   $203.90  
  7 purchase totals = $1,053.54       $1,149.6052   $1,149.61   $1,149.60   $1,149.60