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 $66.58   12.552%   $74.9371   $74.94   $74.95   $74.90  
  Purchase #2 $69.84   8.837%   $76.0118   $76.01   $76.00   $76.00  
  Purchase #3 $59.57   8.556%   $64.6668   $64.67   $64.65   $64.70  
  Purchase #4 $26.31   12.604%   $29.6261   $29.63   $29.65   $29.60  
  Purchase #5 $234.63   9.730%   $257.4595   $257.46   $257.45   $257.50  
  Purchase #6 $24.25   9.157%   $26.4706   $26.47   $26.45   $26.50  
  Purchase #7 $42.44   8.743%   $46.1505   $46.15   $46.15   $46.20  
  7 purchase totals = $523.62       $575.3224   $575.33   $575.30   $575.40