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 $239.44   13.180%   $270.9982   $271.00   $271.00   $271.00  
  Purchase #2 $220.59   4.386%   $230.2651   $230.27   $230.25   $230.30  
  Purchase #3 $61.75   4.726%   $64.6683   $64.67   $64.65   $64.70  
  Purchase #4 $50.51   4.239%   $52.6511   $52.65   $52.65   $52.70  
  Purchase #5 $240.80   5.672%   $254.4582   $254.46   $254.45   $254.50  
  Purchase #6 $150.90   5.822%   $159.6854   $159.69   $159.70   $159.70  
  Purchase #7 $157.94   8.575%   $171.4834   $171.48   $171.50   $171.50  
  7 purchase totals = $1,121.93       $1,204.2097   $1,204.22   $1,204.20   $1,204.40