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 $222.64   9.543%   $243.8865   $243.89   $243.90   $243.90  
  Purchase #2 $47.36   9.478%   $51.8488   $51.85   $51.85   $51.80  
  Purchase #3 $66.36   5.664%   $70.1186   $70.12   $70.10   $70.10  
  Purchase #4 $37.28   11.852%   $41.6984   $41.70   $41.70   $41.70  
  Purchase #5 $18.83   7.156%   $20.1775   $20.18   $20.20   $20.20  
  Purchase #6 $43.35   9.440%   $47.4422   $47.44   $47.45   $47.40  
  Purchase #7 $167.88   3.320%   $173.4536   $173.45   $173.45   $173.50  
  7 purchase totals = $603.70       $648.6256   $648.63   $648.65   $648.60