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 $16.30   10.850%   $18.0686   $18.07   $18.05   $18.10  
  Purchase #2 $61.99   9.858%   $68.101   $68.10   $68.10   $68.10  
  Purchase #3 $215.82   10.178%   $237.7862   $237.79   $237.80   $237.80  
  Purchase #4 $39.59   12.613%   $44.5835   $44.58   $44.60   $44.60  
  Purchase #5 $250.74   10.760%   $277.7196   $277.72   $277.70   $277.70  
  Purchase #6 $91.58   7.217%   $98.1893   $98.19   $98.20   $98.20  
  Purchase #7 $140.29   9.628%   $153.7971   $153.80   $153.80   $153.80  
  7 purchase totals = $816.31       $898.2453   $898.25   $898.25   $898.30