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 $73.38   11.342%   $81.7028   $81.70   $81.70   $81.70  
  Purchase #2 $85.98   9.228%   $93.9142   $93.91   $93.90   $93.90  
  Purchase #3 $209.29   11.119%   $232.561   $232.56   $232.55   $232.60  
  Purchase #4 $179.62   9.254%   $196.242   $196.24   $196.25   $196.20  
  Purchase #5 $70.61   3.339%   $72.9677   $72.97   $72.95   $73.00  
  Purchase #6 $235.83   9.699%   $258.7032   $258.70   $258.70   $258.70  
  Purchase #7 $134.67   3.178%   $138.9498   $138.95   $138.95   $138.90  
  7 purchase totals = $989.38       $1,075.0407   $1,075.03   $1,075.00   $1,075.00