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 $147.82   13.665%   $168.0196   $168.02   $168.00   $168.00  
  Purchase #2 $133.92   6.593%   $142.7493   $142.75   $142.75   $142.70  
  Purchase #3 $230.57   10.459%   $254.6853   $254.69   $254.70   $254.70  
  Purchase #4 $22.39   6.452%   $23.8346   $23.83   $23.85   $23.80  
  Purchase #5 $183.64   10.605%   $203.115   $203.12   $203.10   $203.10  
  Purchase #6 $177.55   5.296%   $186.953   $186.95   $186.95   $187.00  
  Purchase #7 $160.62   13.411%   $182.1607   $182.16   $182.15   $182.20  
  7 purchase totals = $1,056.51       $1,161.5175   $1,161.52   $1,161.50   $1,161.50