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 $49.52   13.787%   $56.3473   $56.35   $56.35   $56.30  
  Purchase #2 $214.95   6.616%   $229.1711   $229.17   $229.15   $229.20  
  Purchase #3 $113.67   5.168%   $119.5445   $119.54   $119.55   $119.50  
  Purchase #4 $96.34   5.291%   $101.4373   $101.44   $101.45   $101.40  
  Purchase #5 $243.81   9.477%   $266.9159   $266.92   $266.90   $266.90  
  Purchase #6 $85.35   4.489%   $89.1814   $89.18   $89.20   $89.20  
  Purchase #7 $191.88   11.836%   $214.5909   $214.59   $214.60   $214.60  
  7 purchase totals = $995.52       $1,077.1884   $1,077.19   $1,077.20   $1,077.10