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 $58.31   11.514%   $65.0238   $65.02   $65.00   $65.00  
  Purchase #2 $220.62   12.185%   $247.5025   $247.50   $247.50   $247.50  
  Purchase #3 $138.34   3.520%   $143.2096   $143.21   $143.20   $143.20  
  Purchase #4 $62.32   9.160%   $68.0285   $68.03   $68.05   $68.00  
  Purchase #5 $236.37   5.824%   $250.1362   $250.14   $250.15   $250.10  
  Purchase #6 $250.40   12.319%   $281.2468   $281.25   $281.25   $281.20  
  Purchase #7 $208.39   10.479%   $230.2272   $230.23   $230.25   $230.20  
  7 purchase totals = $1,174.75       $1,285.3746   $1,285.38   $1,285.40   $1,285.20