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 $56.74   5.124%   $59.6474   $59.65   $59.65   $59.60  
  Purchase #2 $128.69   10.855%   $142.6593   $142.66   $142.65   $142.70  
  Purchase #3 $73.36   11.222%   $81.5925   $81.59   $81.60   $81.60  
  Purchase #4 $112.31   8.149%   $121.4621   $121.46   $121.45   $121.50  
  Purchase #5 $204.52   3.551%   $211.7825   $211.78   $211.80   $211.80  
  Purchase #6 $238.62   7.858%   $257.3708   $257.37   $257.35   $257.40  
  Purchase #7 $74.84   13.728%   $85.114   $85.11   $85.10   $85.10  
  7 purchase totals = $889.08       $959.6286   $959.62   $959.60   $959.70