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 $192.68   13.121%   $217.9615   $217.96   $217.95   $218.00  
  Purchase #2 $221.63   8.130%   $239.6485   $239.65   $239.65   $239.60  
  Purchase #3 $49.32   6.145%   $52.3507   $52.35   $52.35   $52.40  
  Purchase #4 $152.37   10.541%   $168.4313   $168.43   $168.45   $168.40  
  Purchase #5 $173.75   5.634%   $183.5391   $183.54   $183.55   $183.50  
  Purchase #6 $142.97   3.320%   $147.7166   $147.72   $147.70   $147.70  
  Purchase #7 $249.28   7.571%   $268.153   $268.15   $268.15   $268.20  
  7 purchase totals = $1,182.00       $1,277.8007   $1,277.80   $1,277.80   $1,277.80