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 $44.50   4.467%   $46.4878   $46.49   $46.50   $46.50  
  Purchase #2 $67.41   10.839%   $74.7166   $74.72   $74.70   $74.70  
  Purchase #3 $195.76   7.466%   $210.3754   $210.38   $210.40   $210.40  
  Purchase #4 $197.78   6.842%   $211.3121   $211.31   $211.30   $211.30  
  Purchase #5 $193.75   4.539%   $202.5443   $202.54   $202.55   $202.50  
  Purchase #6 $22.89   9.602%   $25.0879   $25.09   $25.10   $25.10  
  Purchase #7 $33.91   12.650%   $38.1996   $38.20   $38.20   $38.20  
  7 purchase totals = $756.00       $808.7237   $808.73   $808.75   $808.70