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 $44.46   9.398%   $48.6384   $48.64   $48.65   $48.60  
  Purchase #2 $97.62   11.585%   $108.9293   $108.93   $108.95   $108.90  
  Purchase #3 $149.30   9.148%   $162.958   $162.96   $162.95   $163.00  
  Purchase #4 $177.51   5.857%   $187.9068   $187.91   $187.90   $187.90  
  Purchase #5 $173.84   10.425%   $191.9628   $191.96   $191.95   $192.00  
  Purchase #6 $32.52   13.496%   $36.9089   $36.91   $36.90   $36.90  
  Purchase #7 $218.66   3.672%   $226.6892   $226.69   $226.70   $226.70  
  7 purchase totals = $893.91       $963.9934   $964.00   $964.00   $964.00