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 $123.47   7.190%   $132.3475   $132.35   $132.35   $132.30  
  Purchase #2 $88.75   8.166%   $95.9973   $96.00   $96.00   $96.00  
  Purchase #3 $105.49   10.502%   $116.5686   $116.57   $116.55   $116.60  
  Purchase #4 $209.36   5.669%   $221.2286   $221.23   $221.25   $221.20  
  Purchase #5 $24.95   5.686%   $26.3687   $26.37   $26.35   $26.40  
  Purchase #6 $43.59   11.265%   $48.5004   $48.50   $48.50   $48.50  
  Purchase #7 $18.91   5.861%   $20.0183   $20.02   $20.00   $20.00  
  7 purchase totals = $614.52       $661.0294   $661.04   $661.00   $661.00