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 $37.76   7.560%   $40.6147   $40.61   $40.60   $40.60  
  Purchase #2 $158.52   10.804%   $175.6465   $175.65   $175.65   $175.60  
  Purchase #3 $107.88   6.332%   $114.711   $114.71   $114.70   $114.70  
  Purchase #4 $94.57   6.832%   $101.031   $101.03   $101.05   $101.00  
  Purchase #5 $229.33   7.596%   $246.7499   $246.75   $246.75   $246.70  
  Purchase #6 $22.99   6.365%   $24.4533   $24.45   $24.45   $24.50  
  Purchase #7 $109.40   9.775%   $120.0939   $120.09   $120.10   $120.10  
  7 purchase totals = $760.45       $823.3003   $823.29   $823.30   $823.20