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 $32.73   6.253%   $34.7766   $34.78   $34.80   $34.80  
  Purchase #2 $134.94   5.721%   $142.6599   $142.66   $142.65   $142.70  
  Purchase #3 $245.67   8.107%   $265.5865   $265.59   $265.60   $265.60  
  Purchase #4 $111.40   10.842%   $123.478   $123.48   $123.50   $123.50  
  Purchase #5 $118.43   6.541%   $126.1765   $126.18   $126.20   $126.20  
  Purchase #6 $22.67   13.181%   $25.6581   $25.66   $25.65   $25.70  
  Purchase #7 $26.76   3.602%   $27.7239   $27.72   $27.70   $27.70  
  7 purchase totals = $692.60       $746.0595   $746.07   $746.10   $746.20