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 $42.72   5.840%   $45.2148   $45.21   $45.20   $45.20  
  Purchase #2 $45.70   7.744%   $49.239   $49.24   $49.25   $49.20  
  Purchase #3 $231.40   11.819%   $258.7492   $258.75   $258.75   $258.70  
  Purchase #4 $103.71   4.229%   $108.0959   $108.10   $108.10   $108.10  
  Purchase #5 $211.48   13.432%   $239.886   $239.89   $239.90   $239.90  
  Purchase #6 $118.59   12.348%   $133.2335   $133.23   $133.25   $133.20  
  Purchase #7 $105.70   3.396%   $109.2896   $109.29   $109.30   $109.30  
  7 purchase totals = $859.30       $943.7080   $943.71   $943.75   $943.60