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 $90.34   8.487%   $98.0072   $98.01   $98.00   $98.00  
  Purchase #2 $20.77   12.385%   $23.3424   $23.34   $23.35   $23.30  
  Purchase #3 $88.51   5.255%   $93.1612   $93.16   $93.15   $93.20  
  Purchase #4 $22.96   4.422%   $23.9753   $23.98   $24.00   $24.00  
  Purchase #5 $203.62   3.839%   $211.437   $211.44   $211.45   $211.40  
  Purchase #6 $176.93   8.693%   $192.3105   $192.31   $192.30   $192.30  
  Purchase #7 $64.91   6.453%   $69.0986   $69.10   $69.10   $69.10  
  7 purchase totals = $668.04       $711.3322   $711.34   $711.35   $711.30