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 $33.91   4.864%   $35.5594   $35.56   $35.55   $35.60  
  Purchase #2 $241.34   12.441%   $271.3651   $271.37   $271.35   $271.40  
  Purchase #3 $133.75   10.408%   $147.6707   $147.67   $147.65   $147.70  
  Purchase #4 $243.55   8.322%   $263.8182   $263.82   $263.80   $263.80  
  Purchase #5 $234.55   3.640%   $243.0876   $243.09   $243.10   $243.10  
  Purchase #6 $229.34   8.501%   $248.8362   $248.84   $248.85   $248.80  
  Purchase #7 $57.68   5.724%   $60.9816   $60.98   $61.00   $61.00  
  7 purchase totals = $1,174.12       $1,271.3188   $1,271.33   $1,271.30   $1,271.40