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 $249.98   7.635%   $269.066   $269.07   $269.05   $269.10  
  Purchase #2 $134.53   3.218%   $138.8592   $138.86   $138.85   $138.90  
  Purchase #3 $40.49   6.636%   $43.1769   $43.18   $43.20   $43.20  
  Purchase #4 $234.56   3.578%   $242.9526   $242.95   $242.95   $243.00  
  Purchase #5 $54.58   8.405%   $59.1674   $59.17   $59.15   $59.20  
  Purchase #6 $175.39   6.145%   $186.1677   $186.17   $186.15   $186.20  
  Purchase #7 $60.26   7.753%   $64.932   $64.93   $64.95   $64.90  
  7 purchase totals = $949.79       $1,004.3218   $1,004.33   $1,004.30   $1,004.50