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 $221.42   11.130%   $246.064   $246.06   $246.05   $246.10  
  Purchase #2 $127.87   11.840%   $143.0098   $143.01   $143.00   $143.00  
  Purchase #3 $71.92   10.243%   $79.2868   $79.29   $79.30   $79.30  
  Purchase #4 $243.37   6.595%   $259.4203   $259.42   $259.40   $259.40  
  Purchase #5 $222.32   9.452%   $243.3337   $243.33   $243.35   $243.30  
  Purchase #6 $163.54   9.745%   $179.477   $179.48   $179.50   $179.50  
  Purchase #7 $34.52   5.701%   $36.488   $36.49   $36.50   $36.50  
  7 purchase totals = $1,084.96       $1,187.0796   $1,187.08   $1,187.10   $1,187.10