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 $10.83   7.362%   $11.6273   $11.63   $11.65   $11.60  
  Purchase #2 $212.71   6.739%   $227.0445   $227.04   $227.05   $227.00  
  Purchase #3 $85.28   10.405%   $94.1534   $94.15   $94.15   $94.20  
  Purchase #4 $250.98   9.231%   $274.148   $274.15   $274.15   $274.10  
  Purchase #5 $34.32   11.196%   $38.1625   $38.16   $38.15   $38.20  
  Purchase #6 $53.91   8.685%   $58.5921   $58.59   $58.60   $58.60  
  Purchase #7 $218.91   11.133%   $243.2813   $243.28   $243.30   $243.30  
  7 purchase totals = $866.94       $947.0091   $947.00   $947.05   $947.00