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 $53.27   11.808%   $59.5601   $59.56   $59.55   $59.60  
  Purchase #2 $157.53   13.593%   $178.9431   $178.94   $178.95   $178.90  
  Purchase #3 $173.60   7.194%   $186.0888   $186.09   $186.10   $186.10  
  Purchase #4 $103.86   3.242%   $107.2271   $107.23   $107.25   $107.20  
  Purchase #5 $146.27   6.815%   $156.2383   $156.24   $156.25   $156.20  
  Purchase #6 $94.30   7.769%   $101.6262   $101.63   $101.65   $101.60  
  Purchase #7 $249.75   6.829%   $266.8054   $266.81   $266.80   $266.80  
  7 purchase totals = $978.58       $1,056.4890   $1,056.50   $1,056.55   $1,056.40