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 $223.26   9.134%   $243.6526   $243.65   $243.65   $243.70  
  Purchase #2 $21.75   11.723%   $24.2998   $24.30   $24.30   $24.30  
  Purchase #3 $107.88   9.534%   $118.1653   $118.17   $118.15   $118.20  
  Purchase #4 $194.66   11.674%   $217.3846   $217.38   $217.40   $217.40  
  Purchase #5 $65.89   8.308%   $71.3641   $71.36   $71.35   $71.40  
  Purchase #6 $234.52   11.357%   $261.1544   $261.15   $261.15   $261.20  
  Purchase #7 $143.79   11.564%   $160.4179   $160.42   $160.40   $160.40  
  7 purchase totals = $991.75       $1,096.4387   $1,096.43   $1,096.40   $1,096.60