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 $64.36   8.521%   $69.8441   $69.84   $69.85   $69.80  
  Purchase #2 $87.57   7.832%   $94.4285   $94.43   $94.45   $94.40  
  Purchase #3 $24.93   9.798%   $27.3726   $27.37   $27.35   $27.40  
  Purchase #4 $88.94   12.827%   $100.3483   $100.35   $100.35   $100.30  
  Purchase #5 $153.79   9.353%   $168.174   $168.17   $168.15   $168.20  
  Purchase #6 $192.89   4.205%   $201.001   $201.00   $201.00   $201.00  
  Purchase #7 $104.86   8.473%   $113.7448   $113.74   $113.75   $113.70  
  7 purchase totals = $717.34       $774.9133   $774.90   $774.90   $774.80