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 $54.29   13.377%   $61.5524   $61.55   $61.55   $61.60  
  Purchase #2 $62.98   5.577%   $66.4924   $66.49   $66.50   $66.50  
  Purchase #3 $204.59   10.463%   $225.9963   $226.00   $226.00   $226.00  
  Purchase #4 $49.43   9.128%   $53.942   $53.94   $53.95   $53.90  
  Purchase #5 $85.62   4.460%   $89.4387   $89.44   $89.45   $89.40  
  Purchase #6 $68.56   9.717%   $75.222   $75.22   $75.20   $75.20  
  Purchase #7 $239.82   7.102%   $256.852   $256.85   $256.85   $256.90  
  7 purchase totals = $765.29       $829.4958   $829.49   $829.50   $829.50