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 $206.32   11.110%   $229.2422   $229.24   $229.25   $229.20  
  Purchase #2 $241.60   3.183%   $249.2901   $249.29   $249.30   $249.30  
  Purchase #3 $39.46   7.832%   $42.5505   $42.55   $42.55   $42.60  
  Purchase #4 $174.44   3.465%   $180.4843   $180.48   $180.50   $180.50  
  Purchase #5 $217.57   13.208%   $246.3066   $246.31   $246.30   $246.30  
  Purchase #6 $184.45   4.463%   $192.682   $192.68   $192.70   $192.70  
  Purchase #7 $59.91   11.319%   $66.6912   $66.69   $66.70   $66.70  
  7 purchase totals = $1,123.75       $1,207.2469   $1,207.24   $1,207.30   $1,207.30