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 $62.78   3.658%   $65.0765   $65.08   $65.10   $65.10  
  Purchase #2 $169.76   10.557%   $187.6816   $187.68   $187.70   $187.70  
  Purchase #3 $201.28   9.751%   $220.9068   $220.91   $220.90   $220.90  
  Purchase #4 $17.52   11.691%   $19.5683   $19.57   $19.55   $19.60  
  Purchase #5 $155.80   4.734%   $163.1756   $163.18   $163.20   $163.20  
  Purchase #6 $105.43   8.507%   $114.3989   $114.40   $114.40   $114.40  
  Purchase #7 $235.36   7.591%   $253.2262   $253.23   $253.25   $253.20  
  7 purchase totals = $947.93       $1,024.0339   $1,024.05   $1,024.10   $1,024.10