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 $41.91   8.764%   $45.583   $45.58   $45.60   $45.60  
  Purchase #2 $115.49   8.301%   $125.0768   $125.08   $125.10   $125.10  
  Purchase #3 $201.36   6.128%   $213.6993   $213.70   $213.70   $213.70  
  Purchase #4 $8.30   6.379%   $8.8295   $8.83   $8.85   $8.80  
  Purchase #5 $39.63   5.446%   $41.7882   $41.79   $41.80   $41.80  
  Purchase #6 $209.73   6.641%   $223.6582   $223.66   $223.65   $223.70  
  Purchase #7 $156.75   9.196%   $171.1647   $171.16   $171.15   $171.20  
  7 purchase totals = $773.17       $829.7997   $829.80   $829.85   $829.90