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 $245.26   9.143%   $267.6841   $267.68   $267.70   $267.70  
  Purchase #2 $95.37   8.384%   $103.3658   $103.37   $103.35   $103.40  
  Purchase #3 $115.46   4.289%   $120.4121   $120.41   $120.40   $120.40  
  Purchase #4 $45.26   7.158%   $48.4997   $48.50   $48.50   $48.50  
  Purchase #5 $200.33   6.559%   $213.4696   $213.47   $213.45   $213.50  
  Purchase #6 $95.59   11.309%   $106.4003   $106.40   $106.40   $106.40  
  Purchase #7 $29.30   10.176%   $32.2816   $32.28   $32.30   $32.30  
  7 purchase totals = $826.57       $892.1132   $892.11   $892.10   $892.20