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 $220.76   11.116%   $245.2997   $245.30   $245.30   $245.30  
  Purchase #2 $209.54   12.396%   $235.5146   $235.51   $235.50   $235.50  
  Purchase #3 $247.45   12.294%   $277.8715   $277.87   $277.85   $277.90  
  Purchase #4 $37.56   7.655%   $40.4352   $40.44   $40.45   $40.40  
  Purchase #5 $81.78   12.158%   $91.7228   $91.72   $91.70   $91.70  
  Purchase #6 $22.59   3.502%   $23.3811   $23.38   $23.40   $23.40  
  Purchase #7 $135.81   9.747%   $149.0474   $149.05   $149.05   $149.00  
  7 purchase totals = $955.49       $1,063.2723   $1,063.27   $1,063.25   $1,063.20