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 $31.96   5.821%   $33.8204   $33.82   $33.80   $33.80  
  Purchase #2 $221.42   10.181%   $243.9628   $243.96   $243.95   $244.00  
  Purchase #3 $186.32   7.868%   $200.9797   $200.98   $201.00   $201.00  
  Purchase #4 $16.74   11.284%   $18.6289   $18.63   $18.65   $18.60  
  Purchase #5 $65.30   6.869%   $69.7855   $69.79   $69.80   $69.80  
  Purchase #6 $217.81   11.812%   $243.5377   $243.54   $243.55   $243.50  
  Purchase #7 $227.51   7.848%   $245.365   $245.37   $245.35   $245.40  
  7 purchase totals = $967.06       $1,056.0800   $1,056.09   $1,056.10   $1,056.10