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 $105.77   5.273%   $111.3473   $111.35   $111.35   $111.30  
  Purchase #2 $246.49   4.143%   $256.7021   $256.70   $256.70   $256.70  
  Purchase #3 $230.91   4.518%   $241.3425   $241.34   $241.35   $241.30  
  Purchase #4 $244.90   8.571%   $265.8904   $265.89   $265.90   $265.90  
  Purchase #5 $80.43   8.213%   $87.0357   $87.04   $87.05   $87.00  
  Purchase #6 $93.39   8.475%   $101.3048   $101.30   $101.30   $101.30  
  Purchase #7 $190.76   6.849%   $203.8252   $203.83   $203.85   $203.80  
  7 purchase totals = $1,192.65       $1,267.4480   $1,267.45   $1,267.50   $1,267.30