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 $183.76   11.872%   $205.576   $205.58   $205.60   $205.60  
  Purchase #2 $98.45   13.297%   $111.5409   $111.54   $111.55   $111.50  
  Purchase #3 $87.80   4.350%   $91.6193   $91.62   $91.60   $91.60  
  Purchase #4 $105.90   4.706%   $110.8837   $110.88   $110.90   $110.90  
  Purchase #5 $29.57   5.673%   $31.2475   $31.25   $31.25   $31.20  
  Purchase #6 $60.46   4.340%   $63.084   $63.08   $63.10   $63.10  
  Purchase #7 $227.99   3.201%   $235.288   $235.29   $235.30   $235.30  
  7 purchase totals = $793.93       $849.2394   $849.24   $849.30   $849.20