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 $114.93   5.107%   $120.7995   $120.80   $120.80   $120.80  
  Purchase #2 $55.96   4.630%   $58.5509   $58.55   $58.55   $58.60  
  Purchase #3 $31.37   12.277%   $35.2213   $35.22   $35.20   $35.20  
  Purchase #4 $86.42   7.266%   $92.6993   $92.70   $92.70   $92.70  
  Purchase #5 $220.82   6.608%   $235.4118   $235.41   $235.40   $235.40  
  Purchase #6 $98.39   13.665%   $111.835   $111.84   $111.85   $111.80  
  Purchase #7 $18.56   11.368%   $20.6699   $20.67   $20.65   $20.70  
  7 purchase totals = $626.45       $675.1877   $675.19   $675.15   $675.20