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 $226.34   12.683%   $255.0467   $255.05   $255.05   $255.00  
  Purchase #2 $164.52   5.575%   $173.692   $173.69   $173.70   $173.70  
  Purchase #3 $110.36   7.803%   $118.9714   $118.97   $118.95   $119.00  
  Purchase #4 $223.81   4.531%   $233.9508   $233.95   $233.95   $234.00  
  Purchase #5 $119.56   3.701%   $123.9849   $123.98   $124.00   $124.00  
  Purchase #6 $180.91   5.629%   $191.0934   $191.09   $191.10   $191.10  
  Purchase #7 $211.37   8.671%   $229.6979   $229.70   $229.70   $229.70  
  7 purchase totals = $1,236.87       $1,326.4371   $1,326.43   $1,326.45   $1,326.50