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 $52.89   9.490%   $57.9093   $57.91   $57.90   $57.90  
  Purchase #2 $69.73   13.796%   $79.35   $79.35   $79.35   $79.40  
  Purchase #3 $205.94   3.432%   $213.0079   $213.01   $213.00   $213.00  
  Purchase #4 $248.25   5.391%   $261.6332   $261.63   $261.65   $261.60  
  Purchase #5 $185.58   9.397%   $203.019   $203.02   $203.00   $203.00  
  Purchase #6 $82.87   13.541%   $94.0914   $94.09   $94.10   $94.10  
  Purchase #7 $231.50   6.629%   $246.8461   $246.85   $246.85   $246.80  
  7 purchase totals = $1,076.76       $1,155.8569   $1,155.86   $1,155.85   $1,155.80