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 $182.94   6.557%   $194.9354   $194.94   $194.95   $194.90  
  Purchase #2 $142.64   8.548%   $154.8329   $154.83   $154.85   $154.80  
  Purchase #3 $78.88   7.173%   $84.5381   $84.54   $84.55   $84.50  
  Purchase #4 $29.96   11.313%   $33.3494   $33.35   $33.35   $33.30  
  Purchase #5 $80.78   6.697%   $86.1898   $86.19   $86.20   $86.20  
  Purchase #6 $77.34   3.835%   $80.306   $80.31   $80.30   $80.30  
  Purchase #7 $186.88   13.361%   $211.849   $211.85   $211.85   $211.80  
  7 purchase totals = $779.42       $846.0006   $846.01   $846.05   $845.80