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 $180.84   12.111%   $202.7415   $202.74   $202.75   $202.70  
  Purchase #2 $107.77   5.446%   $113.6392   $113.64   $113.65   $113.60  
  Purchase #3 $243.43   12.144%   $272.9921   $272.99   $273.00   $273.00  
  Purchase #4 $63.44   5.550%   $66.9609   $66.96   $66.95   $67.00  
  Purchase #5 $226.82   9.724%   $248.876   $248.88   $248.90   $248.90  
  Purchase #6 $57.35   4.612%   $59.995   $60.00   $60.00   $60.00  
  Purchase #7 $248.42   6.689%   $265.0368   $265.04   $265.05   $265.00  
  7 purchase totals = $1,128.07       $1,230.2415   $1,230.25   $1,230.30   $1,230.20