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 $56.99   13.591%   $64.7355   $64.74   $64.75   $64.70  
  Purchase #2 $219.75   10.833%   $243.5555   $243.56   $243.55   $243.60  
  Purchase #3 $114.76   7.149%   $122.9642   $122.96   $122.95   $123.00  
  Purchase #4 $33.53   3.734%   $34.782   $34.78   $34.80   $34.80  
  Purchase #5 $134.30   6.411%   $142.91   $142.91   $142.90   $142.90  
  Purchase #6 $202.44   4.601%   $211.7543   $211.75   $211.75   $211.80  
  Purchase #7 $80.39   8.873%   $87.523   $87.52   $87.50   $87.50  
  7 purchase totals = $842.16       $908.2245   $908.22   $908.20   $908.30