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 $58.45   5.479%   $61.6525   $61.65   $61.65   $61.70  
  Purchase #2 $161.55   6.793%   $172.5241   $172.52   $172.50   $172.50  
  Purchase #3 $19.34   11.106%   $21.4879   $21.49   $21.50   $21.50  
  Purchase #4 $180.72   9.139%   $197.236   $197.24   $197.25   $197.20  
  Purchase #5 $23.46   11.614%   $26.1846   $26.18   $26.20   $26.20  
  Purchase #6 $53.29   5.863%   $56.4144   $56.41   $56.40   $56.40  
  Purchase #7 $97.46   5.659%   $102.9753   $102.98   $103.00   $103.00  
  7 purchase totals = $594.27       $638.4748   $638.47   $638.50   $638.50