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 $230.28   13.601%   $261.6004   $261.60   $261.60   $261.60  
  Purchase #2 $109.65   7.294%   $117.6479   $117.65   $117.65   $117.60  
  Purchase #3 $167.66   3.174%   $172.9815   $172.98   $173.00   $173.00  
  Purchase #4 $112.51   9.601%   $123.3121   $123.31   $123.30   $123.30  
  Purchase #5 $197.52   12.217%   $221.651   $221.65   $221.65   $221.70  
  Purchase #6 $230.42   7.182%   $246.9688   $246.97   $246.95   $247.00  
  Purchase #7 $185.89   13.505%   $210.9944   $210.99   $211.00   $211.00  
  7 purchase totals = $1,233.93       $1,355.1561   $1,355.15   $1,355.15   $1,355.20