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 $232.49   6.487%   $247.5716   $247.57   $247.55   $247.60  
  Purchase #2 $16.79   4.157%   $17.488   $17.49   $17.50   $17.50  
  Purchase #3 $151.36   8.207%   $163.7821   $163.78   $163.80   $163.80  
  Purchase #4 $246.25   12.589%   $277.2504   $277.25   $277.25   $277.30  
  Purchase #5 $82.51   4.414%   $86.152   $86.15   $86.15   $86.20  
  Purchase #6 $224.48   13.763%   $255.3752   $255.38   $255.40   $255.40  
  Purchase #7 $84.98   8.771%   $92.4336   $92.43   $92.45   $92.40  
  7 purchase totals = $1,038.86       $1,140.0529   $1,140.05   $1,140.10   $1,140.20