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 $66.96   11.283%   $74.5151   $74.52   $74.50   $74.50  
  Purchase #2 $134.86   9.574%   $147.7715   $147.77   $147.75   $147.80  
  Purchase #3 $47.32   12.147%   $53.068   $53.07   $53.05   $53.10  
  Purchase #4 $63.53   3.606%   $65.8209   $65.82   $65.80   $65.80  
  Purchase #5 $226.40   13.759%   $257.5504   $257.55   $257.55   $257.60  
  Purchase #6 $118.71   10.789%   $131.5176   $131.52   $131.50   $131.50  
  Purchase #7 $48.38   8.367%   $52.428   $52.43   $52.45   $52.40  
  7 purchase totals = $706.16       $782.6715   $782.68   $782.60   $782.70