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 $139.65   12.585%   $157.225   $157.23   $157.25   $157.20  
  Purchase #2 $219.40   13.221%   $248.4069   $248.41   $248.40   $248.40  
  Purchase #3 $87.73   5.482%   $92.5394   $92.54   $92.55   $92.50  
  Purchase #4 $84.84   9.690%   $93.061   $93.06   $93.05   $93.10  
  Purchase #5 $109.72   3.577%   $113.6447   $113.64   $113.65   $113.60  
  Purchase #6 $60.98   8.324%   $66.056   $66.06   $66.05   $66.10  
  Purchase #7 $239.26   6.650%   $255.1708   $255.17   $255.15   $255.20  
  7 purchase totals = $941.58       $1,026.1038   $1,026.11   $1,026.10   $1,026.10