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 $86.85   7.614%   $93.4628   $93.46   $93.45   $93.50  
  Purchase #2 $110.77   5.581%   $116.9521   $116.95   $116.95   $117.00  
  Purchase #3 $71.90   12.163%   $80.6452   $80.65   $80.65   $80.60  
  Purchase #4 $173.91   13.564%   $197.4992   $197.50   $197.50   $197.50  
  Purchase #5 $127.96   4.727%   $134.0087   $134.01   $134.00   $134.00  
  Purchase #6 $236.54   3.114%   $243.9059   $243.91   $243.90   $243.90  
  Purchase #7 $164.81   13.104%   $186.4067   $186.41   $186.40   $186.40  
  7 purchase totals = $972.74       $1,052.8806   $1,052.89   $1,052.85   $1,052.90