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 $75.65   8.217%   $81.8662   $81.87   $81.85   $81.90  
  Purchase #2 $200.48   10.391%   $221.3119   $221.31   $221.30   $221.30  
  Purchase #3 $135.64   13.685%   $154.2023   $154.20   $154.20   $154.20  
  Purchase #4 $80.61   13.268%   $91.3053   $91.31   $91.30   $91.30  
  Purchase #5 $202.97   8.218%   $219.6501   $219.65   $219.65   $219.70  
  Purchase #6 $111.38   4.766%   $116.6884   $116.69   $116.70   $116.70  
  Purchase #7 $139.86   5.534%   $147.5999   $147.60   $147.60   $147.60  
  7 purchase totals = $946.59       $1,032.6241   $1,032.63   $1,032.60   $1,032.70