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 $150.53   8.122%   $162.756   $162.76   $162.75   $162.80  
  Purchase #2 $14.60   11.367%   $16.2596   $16.26   $16.25   $16.30  
  Purchase #3 $50.65   9.654%   $55.5398   $55.54   $55.55   $55.50  
  Purchase #4 $35.90   3.662%   $37.2147   $37.21   $37.20   $37.20  
  Purchase #5 $231.28   6.587%   $246.5144   $246.51   $246.50   $246.50  
  Purchase #6 $173.94   12.374%   $195.4633   $195.46   $195.45   $195.50  
  Purchase #7 $231.74   13.466%   $262.9461   $262.95   $262.95   $262.90  
  7 purchase totals = $888.64       $976.6939   $976.69   $976.65   $976.70