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 $68.38   11.279%   $76.0926   $76.09   $76.10   $76.10  
  Purchase #2 $153.26   7.442%   $164.6656   $164.67   $164.65   $164.70  
  Purchase #3 $132.50   13.197%   $149.986   $149.99   $150.00   $150.00  
  Purchase #4 $68.86   4.208%   $71.7576   $71.76   $71.75   $71.80  
  Purchase #5 $180.93   13.277%   $204.9521   $204.95   $204.95   $205.00  
  Purchase #6 $212.69   3.242%   $219.5854   $219.59   $219.60   $219.60  
  Purchase #7 $24.46   4.279%   $25.5066   $25.51   $25.50   $25.50  
  7 purchase totals = $841.08       $912.5459   $912.56   $912.55   $912.70