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 $196.26   13.724%   $223.1947   $223.19   $223.20   $223.20  
  Purchase #2 $91.94   8.372%   $99.6372   $99.64   $99.65   $99.60  
  Purchase #3 $168.54   4.564%   $176.2322   $176.23   $176.25   $176.20  
  Purchase #4 $138.52   6.322%   $147.2772   $147.28   $147.30   $147.30  
  Purchase #5 $130.96   7.811%   $141.1893   $141.19   $141.20   $141.20  
  Purchase #6 $163.28   5.364%   $172.0383   $172.04   $172.05   $172.00  
  Purchase #7 $79.59   9.767%   $87.3636   $87.36   $87.35   $87.40  
  7 purchase totals = $969.09       $1,046.9325   $1,046.93   $1,047.00   $1,046.90