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 $58.46   8.651%   $63.5174   $63.52   $63.50   $63.50  
  Purchase #2 $55.39   8.111%   $59.8827   $59.88   $59.90   $59.90  
  Purchase #3 $36.45   4.108%   $37.9474   $37.95   $37.95   $37.90  
  Purchase #4 $60.45   6.511%   $64.3859   $64.39   $64.40   $64.40  
  Purchase #5 $88.55   8.721%   $96.2724   $96.27   $96.25   $96.30  
  Purchase #6 $15.50   8.418%   $16.8048   $16.80   $16.80   $16.80  
  Purchase #7 $217.40   10.131%   $239.4248   $239.42   $239.40   $239.40  
  7 purchase totals = $532.20       $578.2354   $578.23   $578.20   $578.20