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 $115.43   6.564%   $123.0068   $123.01   $123.00   $123.00  
  Purchase #2 $61.65   11.361%   $68.6541   $68.65   $68.65   $68.70  
  Purchase #3 $114.30   5.474%   $120.5568   $120.56   $120.55   $120.60  
  Purchase #4 $19.88   12.143%   $22.294   $22.29   $22.30   $22.30  
  Purchase #5 $96.49   7.813%   $104.0288   $104.03   $104.05   $104.00  
  Purchase #6 $91.93   13.647%   $104.4757   $104.48   $104.50   $104.50  
  Purchase #7 $79.91   4.373%   $83.4045   $83.40   $83.40   $83.40  
  7 purchase totals = $579.59       $626.4207   $626.42   $626.45   $626.50