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 $55.47   8.839%   $60.373   $60.37   $60.35   $60.40  
  Purchase #2 $186.39   9.646%   $204.3692   $204.37   $204.35   $204.40  
  Purchase #3 $19.35   3.607%   $20.048   $20.05   $20.05   $20.00  
  Purchase #4 $163.78   7.748%   $176.4697   $176.47   $176.45   $176.50  
  Purchase #5 $88.40   10.510%   $97.6908   $97.69   $97.70   $97.70  
  Purchase #6 $243.85   8.308%   $264.1091   $264.11   $264.10   $264.10  
  Purchase #7 $38.96   11.483%   $43.4338   $43.43   $43.45   $43.40  
  7 purchase totals = $796.20       $866.4936   $866.49   $866.45   $866.50