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 $240.84   11.487%   $268.5053   $268.51   $268.50   $268.50  
  Purchase #2 $152.37   4.510%   $159.2419   $159.24   $159.25   $159.20  
  Purchase #3 $50.72   10.855%   $56.2257   $56.23   $56.25   $56.20  
  Purchase #4 $163.82   7.487%   $176.0852   $176.09   $176.10   $176.10  
  Purchase #5 $24.74   7.378%   $26.5653   $26.57   $26.55   $26.60  
  Purchase #6 $99.43   10.331%   $109.7021   $109.70   $109.70   $109.70  
  Purchase #7 $230.40   10.246%   $254.0068   $254.01   $254.00   $254.00  
  7 purchase totals = $962.32       $1,050.3323   $1,050.35   $1,050.35   $1,050.30