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 $244.50   5.737%   $258.527   $258.53   $258.55   $258.50  
  Purchase #2 $152.38   13.283%   $172.6206   $172.62   $172.60   $172.60  
  Purchase #3 $244.60   13.243%   $276.9924   $276.99   $277.00   $277.00  
  Purchase #4 $160.76   11.505%   $179.2554   $179.26   $179.25   $179.30  
  Purchase #5 $22.97   5.865%   $24.3172   $24.32   $24.30   $24.30  
  Purchase #6 $160.55   10.242%   $176.9935   $176.99   $177.00   $177.00  
  Purchase #7 $175.94   3.199%   $181.5683   $181.57   $181.55   $181.60  
  7 purchase totals = $1,161.70       $1,270.2744   $1,270.28   $1,270.25   $1,270.30