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 $62.52   13.378%   $70.8839   $70.88   $70.90   $70.90  
  Purchase #2 $219.47   7.387%   $235.6822   $235.68   $235.70   $235.70  
  Purchase #3 $231.75   9.593%   $253.9818   $253.98   $254.00   $254.00  
  Purchase #4 $243.34   7.189%   $260.8337   $260.83   $260.85   $260.80  
  Purchase #5 $210.32   11.737%   $235.0053   $235.01   $235.00   $235.00  
  Purchase #6 $134.82   8.608%   $146.4253   $146.43   $146.45   $146.40  
  Purchase #7 $163.73   13.601%   $185.9989   $186.00   $186.00   $186.00  
  7 purchase totals = $1,265.95       $1,388.8111   $1,388.81   $1,388.90   $1,388.80