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 $62.74   13.555%   $71.2444   $71.24   $71.25   $71.20  
  Purchase #2 $186.42   13.647%   $211.8607   $211.86   $211.85   $211.90  
  Purchase #3 $94.84   6.639%   $101.1364   $101.14   $101.15   $101.10  
  Purchase #4 $211.95   8.752%   $230.4999   $230.50   $230.50   $230.50  
  Purchase #5 $158.81   11.724%   $177.4289   $177.43   $177.45   $177.40  
  Purchase #6 $172.59   5.450%   $181.9962   $182.00   $182.00   $182.00  
  Purchase #7 $33.95   11.642%   $37.9025   $37.90   $37.90   $37.90  
  7 purchase totals = $921.30       $1,012.0690   $1,012.07   $1,012.10   $1,012.00