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 $226.69   3.783%   $235.2657   $235.27   $235.25   $235.30  
  Purchase #2 $64.55   8.446%   $70.0019   $70.00   $70.00   $70.00  
  Purchase #3 $144.26   12.265%   $161.9535   $161.95   $161.95   $162.00  
  Purchase #4 $135.45   12.627%   $152.5533   $152.55   $152.55   $152.60  
  Purchase #5 $184.77   9.524%   $202.3675   $202.37   $202.35   $202.40  
  Purchase #6 $155.39   4.537%   $162.44   $162.44   $162.45   $162.40  
  Purchase #7 $102.64   13.790%   $116.7941   $116.79   $116.80   $116.80  
  7 purchase totals = $1,013.75       $1,101.3760   $1,101.37   $1,101.35   $1,101.50