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 $23.93   10.624%   $26.4723   $26.47   $26.45   $26.50  
  Purchase #2 $20.52   9.530%   $22.4756   $22.48   $22.50   $22.50  
  Purchase #3 $147.29   9.330%   $161.0322   $161.03   $161.05   $161.00  
  Purchase #4 $161.46   6.612%   $172.1357   $172.14   $172.15   $172.10  
  Purchase #5 $61.48   5.798%   $65.0446   $65.04   $65.05   $65.00  
  Purchase #6 $59.76   9.559%   $65.4725   $65.47   $65.45   $65.50  
  Purchase #7 $232.98   7.436%   $250.3044   $250.30   $250.30   $250.30  
  7 purchase totals = $707.42       $762.9373   $762.93   $762.95   $762.90